It doesn't work that way.

As an example last year Canon announced a 15mp point and shoot. People found that the old 10mp version had the same sharpness, except the files were a lot smaller, it was faster, etc. So last week Canon announced a new version, but this time they went back to 10mp.

The extra megapixels don't actually add more sharpness, they just add more pixels to blurry pictures. If you have a sensor designed from the beginning with larger pixels then you can increase the sensitivity, which gives you sharper pictures. You can increase the sensitivity on a high megapixel camera as well, but because the individual pixels are so small, you will get noise. The camera will try to correct for noise by blurring the picture, so now you are back to where you started.