Sharpness: EF 70-200mm F/2.8L IS USM - Full Frame vs APS-C

[prodigy2k7]

I thought there was no difference in quality or sharpness on full frame? Normally full frame the corners seem to get some CA and other junk. And full frame normally has better ISO performance. But what makes a full frame better in sharpness?
Specifically:
Canon 5D
Canon 40D
w/ EF 70-200mm F/2.8 IS USM
Both stopped down to F/5.6 at 70mm

The 5D is a whole "color" sharper (blue) while the 40D is all green.

http://www.dpreview.com/lensreviews...izontal&&config=LensReviewConfiguration.xml?2

 

[jamesino]

From their website:

"
Eagle-eyed viewers will no doubt have noticed that the MTF50 sharpness data at any particular focal length/aperture combination is distinctly higher on full-frame when compared to APS-C. This may at first sight appear unexpected, but in fact is an inevitable consequence of our presentation of the sharpness data in terms of line pairs per picture height (and thus independent of format size).
Quite simply, at any given focal length and aperture, the lens will have a fixed MTF50 profile when expressed in terms of line pairs per millimeter. In order to convert to lp/ph, we have to multiply by the sensor height (in mm); as the full-frame sensor is 1.6x larger, MTF50 should therefore be 1.6x higher.
In practice this is an oversimplification; our tests measure system MTF rather than purely lens MTF, and at frequencies close to Nyquist the camera's anti-aliasing filter will have a significant effect in attenuating the measured MTF50. In addition, our testing procedure involves shooting a chart of fixed size, which therefore requires a closer shooting distance on full frame, and this will also have some influence on the MTF50 data."

 

[prodigy2k7]

Okay so, when comparing full frame to APS-C its not entirely accurate? So, which is more accurate for the lens? FF or Crop? What does that mean in layman's terms anyway?