I was under the impression that by 3d games he meant traditional 3 dimensional games like your generic FPS games - Crysis, Crysis2, TF2, MOH etc. If indeed he meant 3d in the sense of having a 3d capable monitor and sitting in front of it wearing some geeky looking goggles then you are right, nvidia may be the better option. Personally I can't see the value in it at this stage, maybe in the future my opinion will sway on the matter. I couldn't think of anything worse than having to wear glasses all of the time to remove the double vision effect of 3d.
I'm still rocking my old GTX 260 and surprisingly I am yet to come across any game that it can't tackle admirably (although I haven't tried the Crysis2 demo yet). However after seeing the 5770 in action yesterday I was reminded that ATI does seem to have better image quality in most applications. Forgot to mention I watched Green Zone on the 5770 too and it was perfect in every sense.
It might sound like I'm an ATI fanboy but in reality I've used cards from both factions in the past and have always chosen my purchases on which one had the best value for money at the time. Right now both teams have fantastic cards in all price segments which is a win/win for us consumers.