id engines are pretty flexible Cyg.
The new COD games use the Quake 3 engine.
Also, id didn't develop Prey, Quake 4, or Quake Wars. The last game they made was Doom 3.
Comparing it to the UE3 engine?! Ha! Look at Blacksite: Area 51, Mass Effect's frame rate on xbox, etc. UE3 just makes everything shiny. Good engine to make people say ooh and ahh. But not the best thing for great gameplay (Epic knows how to use it, but not many others.)