I have a 7hi and am thinking of upgrading to an A2. However, the dSLR photos I see on these forums seem to have better image quality. I've read this is partly due to the larger SLR sensors. Can someone tell me why prosumer cameras don't (or can't) use APS-sized sensors? I assume it's not a cost issue since an A2 sells for as much as a low-end dSLR.