[stoppingdown]

<p style="font-size:12px;">Wrong. With field curvature the corners will be sharp, unless you are photographing a flat surface covering the whole image frame.

 
Well, indeed it's what I was thinking: consider, for instance, architectural photography in which you're shooting at a building facade (ok, such a photo with a shallow DoF sounds a little weird).
 
But I understand the point, the fact that there is at least one case in which it would be critical doesn't mean it would be always critical and so there's the point to know which of the two defects is involved. Point taken.