People still use C++ to program video games today? Really? I thought everything was going towards Java nowadays... but I am no programmer so I wouldn't know for sure at all.
One word: Speed
The fact that the ps3 went with the cell processor instead of a off the shelf intel processor made programming for it a lot more difficult of a task vs the xbox, and that same reason is why you dont see hardly any cross-console games because programming the two together and making them work happily together is a pain in the balls
Well, assuming you are referring to the Xbox 360, it does not use a x86 (intel) based processor either. Both the Cell and Xenon (used in the 360) are actually PowerPC based architectures.
It's not the CPU that makes it "difficult", it's the development environment and APIs.
You can target both the Xbox 360 and PC using DirectX, meaning it's relatively straightforward to port between those two platforms.
The PlayStation on the other hand, uses OpenGL and other APIs. I would also guess that integration support into Visual Studio is more difficult, as it goes against Microsoft's interests.
But yes, you are right, it's a "pain in the balls" to go cross-platform with the time limits and budgets in the video game development segment.
So how is that an excuse now? The alien technology that is called "Cell" was able to be programmed to communicate with PC's to play Portal 2? PC's have a wide range of hardware... so why would it be any harder to program it to communicate with an Xbox 360? (Besides the point that MS is being a dick about having inferior hardware)
Cross-platform porting issues aside, I read that the real problem is that Microsoft is not keen on letting any competitor onto their "Live" platform.