Why does my 10 megapixel camera let me crop closer and with better clarity than my new 12.1 megapixel camera?

I have a 10 megapixel Canon Powershot Pro1 that I love but which is sometimes to big to easily carry with me. I thought that if I bought the new Sony DSC-W200 with it's 12.1 megapixels, I'd get the same (or better) ability to zoom and crop my pictures (zoom using software/Picasa not the camera zoom). When I compare the two I find that I am able to zoom further in and get much better clarity when zoomed in on pictures taken with the 10 megapixel Canon Powershot Pro1 than when I do this with pictures from my new 12.1 Sony DSC-W200. I've tried to select similiar picture types (in the sun by the water) with similiar focal lengths, but when I zoom in to 100% with the Canon Pro1 I can get much closer to the subject that I can with the Sony. The clarity is also much better on the Canon when zoomed close. What other factors do I need to be considering when looking to get the best ability to crop in close to the pictures subject with greatest clarity?