This is correct. Except when you have 2 or 3 cards in SLI that's when 4GB of VRAM can be fully utilized on a 256 bit bus interface (in current times). Going with a 2GB memory card right now is nonsensical. Next Gen consoles are out, and games very quickly will look prettier on the PC. Soon just like 1.5GB of memory became outdated, and unusable. So will 2GB of memory. It's a very common trend. Not really rocket science.
Telling people to not get a 4GB card right now, because it's on a 256 bit bus interface and that they will run out of power before they run out of VRAM. Is only applicable currently. However, in the very near future you will come to find those same people changing their tune. Not only at 1080p but higher resolutions. Games will use more VRAM. 2GB will become outdated. No reason to invest in a card right now that you can't keep.