Unless the
Nvidia driver page is wrong, that's not quite true. The GTX 285 & 680; GT 120; 8800 GT; Quadro 4000, Quadro K5000 for Mac, Quadro FX 4800 and Quadro FX 5600 are supported. I.e. they only support the official "For Mac" cards. Drivers for the latest and best cards are provided As Is.
So Nvidia is under no obligation to provide or update drivers for the latest and best. Chances are the only reason Nvidia is still turning out drivers is the hope that Apple will start using their chips again.
Given that it has been 6 years since Apple chose an Nvidia card for the Mac Pro and the only Mac Pro that can use Nvidia cards went out of production 3 years ago, the clock may well be ticking. Nvidia could stop producing Mac versions of those drivers tomorrow.