Quote Originally Posted by Sushigaijin
True, but APS pixel density is higher than 4/3 - the 50d's 15 mp is higher than the density of it's closest 4/3 competition, the 10mp E3.

You can rightly say that those are two very different image sizes, but those are the best fit for a camera comparison. based on exact same image sizes, 4/3 will always be more dense.

My point isn't to split hairs but to provide a real-world working example...my point is that you are MORE likely to notice edge distortion on a large sensor than 4/3 pixel density issues in the sweet spot of a lens.
Another point here - most people shooting APS are also using lens in which they pull through the sweet spot. EF-S lens aren't anywhere near as common as the standard EF, and the same with Sony's DT lens. Nikons the only exception with their popular DX lens type.

And well, pixel density can also be a very good thing, my original point was simply that greater pixel density makes the camera much pickier with lens, a very expensive catch 22.