at least, they have to be able to play very well at around 1680x1050 or 1440x900 on one of those lower-power-draw cards (e.g. Nvidia 650 or AMD 7850).
I'm not sure what your desktop resolution is (I'm guessing it's around there). I feel like that's a bit much to expect a computer speced to run a desktop operating system (when using the 3d portion it's only doing basic texturing/compositing) being asked to run modern 3d game at full resolution. Commodity desktop computers have always lagged behind even mainstream modern games. Quake 1 required a floating-point math co-processor I didn't have, then games required 3d cards. There was usually a transition (software rendering mode when 3d cards were needed, PCI 3d cards when AGP started getting popular), but generally they had to be played at a significantly lower resolution and frame rate if they could play at all.
If this model wasn't profitable, they wouldn't be doing it. While there's obviously a market for games like The Sims and Myst (they're some of the top-selling PC games of all time), that's not the same market Crysis 3 is going after.