Comments like the one linked are a great read, but without ANY sourcing what so ever, it's hard to take it seriously.
Certainly, Nvidia is more than happy to donate engineers and code that favours nvidia hardware (as well as the hardware itself) in return for some branding and an exchange of cash, but to claim that it deliberately gimps older or competing hardware seems beyond the realm of likelihood. IF such a thing was happening, there'd be easy ways of proving it and lawsuits would be flying around pretty quickly. Furthermore, ultimately the performance difference in games between similar competing cards is all in line. You get a bit of variance per title, but it's not like 80% difference here, it's a few frames, single-digit percentages.