IIRC, AMD does provide its own compilers - it would make sense for AMD to provide the most efficient method of translating human code to machine code for their own hardware. I think the main issue here is that when applications get compiled, they are usually done with compilers provided by Intel. This may or may not be an indication of wrong-doing on Intel's part, though.
As someone who has a hobby of looking at hardware and a job of writing software, I can say that a very large majority of software developers know next to nothing about the hardware. Just like how many people default to using IE as their browser because they don't know better, almost the same can be applied to developers when it comes to their software.