That's mostly untrue. Half-Life 2 could run on lower end computers and still look fine. It was really well optimized. In fact, the Source engine scales incredibly well. By all accounts Crysis scales really really well as well. Guild Wars can be played on a low end system and look great and then look absolutely amazing on a high end system. Unreal Engine was pretty scalable as well (UE3 not so much I hear though).
Sure there's games where they don't try and optimize them at all and you know what? Most of those are console ports. The worst offenders as of late have been Stranglehold, Gears of War, Lost Planet, and the worst Guitar Hero III. The required specs on GHIII are absolutely ridiculous for the game that it is.
So very true.