Besides the many gameplay enhancements and tweaks made to improve QuakeLive, Carmack said no changes were made to the core game engine form the latest patched version. He went on to explain exactly why this is the case:
"That was a real conscience decision on our part. I'm actually looking through the Quake III code base right now for some ISO development stuff, and I am probably going to have to make some significant changes to get what I want to get out of it. You go in there and you say, 'Oh compile vertex arrays are completely irrelevant nowadays. Everything should be in vertex buffer objects and all this or that.' But the bottom line is it didn't matter at all. Any system today will run the game at 100-125 frames per second cap and any decent system will run it with 4x anti-aliaising.
"So, any significant technology changes that would go in would require new content to wind up taking good advantage of them. And that was one of the things that when we made the transition from Quake 3 to Doom 3, we noticed the content generation patches got so much more expensive. However, we think that there's enough advantages to staying with this level of technology"
"What if" is a trademark of Hewlett Packard, so stop using it in your sentences without permission, or risk being sued.