martin: your comment is true for desktop users, but not for embedded customers.
If you have a fixed application for a product, you have a fixed requirement for speed. That in turn relates to energy consumption and cooling requirements. Of course cost will be an issue - why pay more for something that will do the same job in a 'fixed' environment?
Example - most washing machines used to have 6502s in them (don't know if that's still true). Why? They're powerful, but they're also cheap. Your average washing machine doesn't need to play MP3s, but it does need to do some basic computation, and that was a good balance of cost vs performance.