Hard to say. In my experience:
Dell's failures seem to stem from issues with their casing design. Their casing either falls apart, or restricts airflow to cause it to overheat components which normally wouldn't fail. Not to say there's no issues with parts and other things, but this seems to be the main problem.
HP's failures seem to stem from issues with the design. Though their casing doesn't call apart, those fuckers run really god damn hot. Like, flesh searingly hot. The fact that it has a plastic bottom doesn't bode well for it either. Again, it seems the case is the main problem, but not like there aren't others.
Sony's failures seem to be inconsistent. On occasion, it seems like the casing is an issue. On other occasions, they received faulty parts, then on occasion it seems like the software is screwy and drivers and software begin conflicting with each other. I'm not saying there's a higher instance of failure. I'm saying in my experience, unlike HP and Dell which is very predictable, Sony's failures are a balanced bag of tricks. All you can say in the end is... shit happens. Weirdly enough though, maybe it's just me, I've heard of 3 instances of hotboxed laptops. The only other four instances of hotboxed laptops were all Apple MBAs. I don't know if it's a brand issue or "amazing design", but people like to use those laptops in bed and fuxxor them up doing so!
Lenovos in my experiences I have rarely seen issues. However, the few instances I've seen have generally been corrupted components. HDD and Ram. I am unaware of any other general consistent failures.
Acer in my experiences have rarely failed. Laptops and netbooks alike. But just like Sony, the failures are all a bag of tricks. You never know what will fail. (I've seen clam shell hinges break, HDDs corrupt, ram fail, screen break/crushed, keys falling out etc.)
Asus is another that I have rarely seen issues. However, they do run a bit hotter than normal. Cheap power and performance is what I generally say to people. Issues? It's a coin flip like Sony laptops.
Business Grade:
Sony SZ/Z series are ones I have rarely seen issues with. I use an SZ480 (I think it was) myself. 4 years later, still going strong. Minus the fact I upgraded the HDD and Ram myself. My friend on occasion used to comment that my laptop is the only laptop that could compare in quality to Apple, mainly because it lasted more than the 2 years most individuals own laptops for. I have another theory, I'll say it below. SZ/Z series were built to be light. Moreso ultraportable blood in their systems than rugged powerhouse in other brands. It's light, generally features some type of carbon fibre as a gimmick, but even though it's built in a way that makes you baby it, it performs decently well. There are minor issues with the keyboard in the sense some people think it's too loud, but that's the style, not the performance of it. It can be replaced IIRC.
Sony SR series. Is the series parallel to the SZ series. This one is built more rugged and durable. IIRC, it was playing with magnesium cases in a "sexy way" prior to the new generation Apple notebooks. I believe it featured "island keys" and more powerful video cards than the SZ/Z counterpart.
HP Probook is one sexy beast. The original Envy was the same. The new Envy is pure Apple bandwagon. I had actually hoped to obtain one myself last year boxing day, but at $1000 I decided to purchase something else instead because I already had my own laptop. If the boss isn't going to get me a decent laptop, I'm considering picking one of these up myself if the price is right for studying purposes. The only failures I've ever seen on these things were dead batteries from being over charged, twisted power cables and dented corners. It's built rough and meant for most basic "oops" statements you can chuck at a laptop. I believe most of it was still plastic on the outside, but it was not built in a cheap manner.
Lenovo thinkpads are some fine looking laptops. Ones you can probably do the most damage to (minus Panasonic toughbooks which are pretty much 2x the cost of the same performance) and still feel ok about the laptop. All in all, one of the most reliable laptops I have seen. Failures in these laptops were due to a dice throw at getting a bad component, and a dice throw at aftermarket products. Minus those failures, the laptop still chugs along nicely.
Apple. Not a business grade, but lasts about the same time. In my opinion, their longevity sits with some of their design. I hate the fact the airflow of the exhaust is blocked by the screen when open, however, it seems that this design also keeps individuals from hotboxing their laptops as easily. I don't know if this is intended, but it keeps people from killing MBP and regular macbooks. Another plus is that the case is designed for a bit of a beating. Not as high up there as an idea pad, but at least as high as the typical ruggedness of an ideapad, acer (ie: Net book) or Sony SR series (Which I've always wondered if it was somewhat a basis or competitive product when the new MBP design came out). MBAs on the other hand I've heard of about 4 hotboxes.
Consumer brands in my experience
Sony 1-3 years (With a ridiculous amount of hot boxed ones skewing the numbers. Or individuals upgrading prior to the death of the laptop. Sony's are second hand gifted a lot it seems)
Dell 1-5 years (Nothing over 3 has been free of needing some type of warranty fix from Dell)
HP 1-4 years (With the performance temp of these things, I always wonder how it lasts so long. Constant crashing till death sort of thing.)
Lenovos 1-3 years. Haven't seen too many of them, thus I haven't continually kept track but few failures of them too.
Acer 1-5 years. Generally legacy systems super slow, but still chugging along. Few "deaths". Netbooks are same too. Death usually only occurs on harsh abuse.
Asus 1-? Haven't seen many of them, few hearing instances of death for these though.
Sony business grade. I own an SZ, I know a guy with a Z, and a friend with an SR. Mine is 4 years and chugging without issue. The Z is fine, but the guy prefers his MBP instead. It's about 3 years old IIRC. The SR is fine. 2 years old IIRC.
HP Probook, IIRC, it was replaced when it was 4 years old, much to the anger of the owner. (Corporate laptop). She received some other replacement that died many time afterwards. (They could not replace battery and power cable, so gave her some other shitty one), other than those two, it was fine.
IBM Thinkpad/Lenovo Thinkpad. I don't think I've ever heard of these things dying. That being said, many just "disappear" after a while too. My brother's thinkpad is about 3 years old and works fine. It's too "slow" for him so I might take it off his hands as I stated before, but with a dual core something... it should be good enough for basic tasks with a SSD upgrade. I'd say like 4-5+ before people upgrade because the inner components are too slow.
Apple, usually like 2-4+. It's the warranty. Shit gets fixed all the time, but the laptop keeps chugging so age wise, it's all fair game.
As for Apple and Sony. I'm not sure if it's somehow the design, or just the people who buy them, but people like using these laptops in bed. They hot box them and kill them too. Granted, blocking air intake and exhaust isn't smart. But then again, when did I ever say individuals who buy a certain brand are smart? Also, the "age" of a laptop is also based on the individuals style. People will do things to kill their laptops on purpose. Those ages are also based on how long an individual is WILLING to use their laptop for. This is a huge plus for Apple in general because their OS and programs running on the OS generally will never hit a huge performance glut like running a modern day program on XP that needs increasingly more power every additional year.
