Dude, if the 5870 had 2GB in the first place I wouldn't have had to spend big money on an otherwise tiny upgrade to 6970's. If you want to upgrade every year, or get free video cards, then yeah, VRAM doesn't matter so much. I'd rather upgrade every other year. The 2GB GTX 680 isn't going to get me two years at eyefinity resolution. 4GB probably could.
Indeed, I may push 3 years this time, 04/06/2012 will be 2 years exactly.