I'd be curious to know the actual pixel sizes on the sensor and the optical resolution of the camera's lens(es). It's conceivable (though maybe unlikely) that the optics in the lens could not resolve detail to a level that is smaller than the size of the pixels on the CCD. If that were the case, then the higher pixel count would only capture more of the fuzziness of the lenses -- but what's the point of that?
Additionally, if the pixel sizes are no smaller than those on, say, a 7MP chip, then the only way to capture additional detail is to magnify the image with the lens. Assuming no increase in magnification and no decreasae in pixel size, all you will acquire is a larger frame, not finer detail.
I don't really know very much about consumer or pro-sumer digital cameras, but I would be very surprised to find that the increasing chip resolutions are not due to a decreasing sizes of the individual pixels. That would seem too obvious of a marketing gimmick. I don't have much faith in the camera companies, but well... that would just be too much even for them.