its pretty obvious and plainly simple, you could use those same AA routines, WITH NO ISSUES AT ALL in the demo, final code was changed with the specific intention of removing the ability for ATi to run the code. The code was working, there was no QA issues, there was no testing needed, it worked, Nvidia thought they'd done enough to prevent ATi using AA in the demo, they were wrong, they didn't improve AA the changed the code only to stop ATi cards being able to run it.
That Eidos obviously signed something to allow Nvidia that level of control is disturbing to be honest, but that Nvidia constantly lie about their nasty little tactics is just so much worse.
Hell they'd make more sales by just flat out admiting, yeah, we paid them to make the game better on Nvidia hardware, we have more cash(not true but they can say it) they can truthfully say they pay more money to developers, they can truthfully say they will continue to do this for years to come. Telling people they will constantly try to remove features for ATi users, will only persuade more people to buy Nvidia.
That leaves two options, they are stupid, or the far more likely option, they publically admit thats what they do and ATi/AMD have a serious serious basis for starting an anti-competition lawsuit. So either Nvidia are so utterly stupid its almost impossible to believe(not completely impossible though

) , or even they think what they are doing is borderline illegal and are doing their best to play down the whole issue.