Worthy of note is the fact that the original Intel iMacs and Mac Minis shipped with Mobile processors (Intel Core/Core 2 TXXX rather than EXXX), for the reasons you mention.
Although some iMacs and maybe all iMacs now use desktop-class processors, all Mac minis still have mobile processors. (35 W TDP for the processors in the $599 and the $799 2011 models; 45 W TDP for the CPU in the 2011 Mac mini server.) Otherwise they couldn't be so small and light without overheating!
