The performance may be close in few select games, but you're forgetting that Nvidia (as well as AMD) tries to optimize their drivers for many games and they release the new drivers pretty often... Intel, however, is not very committed to such things (optimizations for wide range of games and frequent driver release), regardless of their future "promises".
But will it be enough to matter? Let's split the difference and say Haswell performs like a GT640, do AMD and Nvidia have anything coming out in the next 3 or 4 months that will draw the same amount of power but perform like a 670?
All i see out there right now is a 730M that is listed to perform like a 640M. AMD has an 8000 series chip out but the only machine I've seen it in is the poster child for all that is wrong with the PC laptop industry.
I know there is a lot of time until Haswell is out, but the press releases, roadmaps and lack of any new architecture on the horizon leave me with a distinct "meh" feeling.