Originally Posted by The_Biz
normal games don't look so jagged without AA turned on, but it seems to particularly affect DOF
A lot of the units in game have quite a low polygon count compared to a lot of other games, this is because the level of detail required for a unit at our normal viewing distance is quite low (90% of all the screenshots we show are from odd zoomed in angles) so this is why you'll notice sharper edges, because your viewing the models from a distance you would not normally be using in game. However Hero units do have a much higher polygon count than average units so you will notice this less on those units.
Low polygon count also allows us to have a such a large population amount. If you look at the screenshots Konstantin posted in the Media forum for May 1st week you'll notice a current popcap limit of 4200 (Note: that number is still a work in progress) that is a lot of units to have onscreen at once because you have to think that you could be playing with say 4 people, so you would have to support up to 16,000 units on screen at once that's a lot for a GPU to process.
We also incorporate both Bloom and HDR (High Dynamic Range) post processing effects, these already take substantial amounts of the GPU's processing power, so AA would add a significant requirement in hardware.