nVidia NEEDS to update drivers on a monthly basis. If you don't use nVidia cards extensively or are a fanboy, then I can see where you might not think that they need them. (24/7 on only two or three games still doesn't give a feel for the rest of the rather large game industry)
However, I would be remiss not to mention the industry wide driver update policy: "Only update your drivers if you have a problem with the current ones".
So while you may not need driver updates personally, nVidia needs to supply them.
Any time a new game comes out, optimizations can be made.
Any time a new game comes out, there is a high probability that at least one card in the three generations supported by the same driver release will have a bug that needs to be fixed.
Finally, any time a new game comes out, there is a chance that nVidia's overaggressive performance focused drivers will drop the ball in the quality department and customers will see the trade off.
Of course they blame it on a driver bug, but the fact of the matter is, if they didn't optimize so aggressively, it wouldn't be a problem in the first place.
Don't think ATI is off the hook either.
nVidia may have led the way with shader replacements, but ATI is just as guilty for stepping down and following suit.
(Shader replacements weren't the first thing nVidia did, just the one that got ATI to take the bait)
I give ATI a slight advantage, though, as they realized that they needed frequent driver updates to make sure the aggressive optimizations didn't get out of hand.
Before someone starts crying fanboy, I should mention that I currently use 3 nVidia based computers and 2 ATI based computers.
Geforce 8800GTS 512Mb
Radeon X1900XT
Quadro FX4500
Geforce 6800 Ultra
AIW Radeon 9700Pro
The Quadro is in an Intel Xeon based system w/Intel chipset.
The rest are in Athlon 64 754/AM2 based systems with nVidia chipsets.