Yeah, pay $1800 and get a 650m, which is the equivalent of a desktop 640, mind you. Which is a very low end card. Sorry, I guess I'm kidding myself; you are getting your money's worth
Or are you talking about the iMac with the 675mx? I mean sure, you can pay $2000 for a 660ti equivalent (mid-high range; not bad). Whatever floats your boat. Although, you could pay half the price and get much better performance and build your own PC. You'll always have the thinnest desktop computer, I guess. (If you can find a use for that)
if your only option is to buy apple notebooks, it gets costly as I noted, if you go for gaming machines you can get much more performance
still I wouldnt chose the 675mx, but the 680mx in the imac