the disk is free. you only pay for the key.
I've begun to hear the opposite now. They now just give you the key free, have a partition, and the DVD costs like 15-30 bucks to obtain. Except for highly expensive comp builds from certain companies.
Sorry, should have been more specific.
If you purchase a copy of Windows separate from a computer you are paying for the license key, not for the disc.
Nor does it violate the Windows EULA to obtain a "clean copy" disc and install that on your HP/Dell/Acer computer and use the license key that came with the computer.
The key isn't "free" when buying a prebuilt, it's part of the cost of the computer. And you're not getting the license directly from MS, you're getting it from whomsoever you got the computer through.
The license key, not the physical disc, is what authorizes you to use the OS.
This is similar to things like Steam where you buy the games and the proof of ownership is the licensing key since no physical disc is present.
Another example: I use a "hacked" copy of Diablo II: LoD, but I use the legit key I got when I bought it. I'm not breaking any rules.