Demonstration of the fact that a higher MP count for the same sensor size does *NOT* require a steadier camera, or less subject motion blur, for the same subject magnification.

The middle image is the original from the native resolution of the Canon XTi, with a 4 pixel software motion blur; the image on the left is the same image downsampled to 50%, with a 2 pixel motion blur applied; the image to the right is the original upsampled to 200%, with an 8 pixel motion blur applied. Both of the synthetic crops (left and right) fully resolved all of the arcs before the blur was applied.

The under-sampled, lowest-MP image suffers the most from the blur, and is inferior in just about every way. The fact that some part of the curves are well-resolved (and all were, before the blur) shows that it is the blur, and not the resolution that does the ultimate damage. The over-sampled, highest-MP image resembles a sensor with pixels with such pixel pitch that the lens is out-resolved by at least 2x, and yet, the same motion blur, relative to the entire frame, ruins detail even less.

More pixels are better for less obtrusive blur, all other things being equal.