Read a pretty good explanation about this a while back. Essentially what the camera companies are doing is creating a higher megapixel on the exact same size sensor. Unfortunately the drawback to this is you're making smaller pixels that in turn get less light which then creates more noise, ect. Seems like the expensive full-frame sensor cameras are the way to go. Higher megapixel counts don't necessarily make a better picture. Then again it's really who's behind the camera that makes the difference too.