> Desktop CPUs are very different: If you can get 10% more performance while doubling power draw, people will just buy bigger coolers and bigger power supplies to go along with the CPU.

No they won't. OEMs will do that to put the 10% higher number on the box ('OC edition!'), but undervolting / powerlimiting has become increasingly popular. Taking a 2-5% haircut on clock frequency lets you reduce power draw by 20-50% for a 1-3% haircut in performance. Suddenly your CPU and GPU are whisper quiet on aircooling.