I think one reason why Carmack still sticks out, is that he set up his company in a way where he can still "play" with new techniques every day. I suspect that not many other programmers have this kind of freedom.

Also, not many other graphic engine programmers have their own company. They might be as good or better as Carmack, but they are hidden under layers of corporate obscurity. The guys at Crytek who invented SSAO come to mind - most of the time SSAO is credited to Crytek and not to individual people (which is a shame, imho).

( SSAO: http://en.wikipedia.org/wiki/Screen_Space_Ambient_Occlusion )