<Evil mode: On>
It's not common sense. They realized they can't increase the pixel count over 12MP without drastically increasing the noise - due to the smaller sensor size.
<Evil mode: Off>
IMO, the resolution should be further increased - there is still more to get from APS-C; but this must be dictated by technological advancements and not by marketing. Other directions, e.g. Foveon-like sensors or methods for extending the DR (Fuji?) should also be explored, of course.
However, the K20D with good lenses is more than enough for me. I won't upgrade for resolution alone, that's a given.