On cameras with higher megapixel counts, the number available in DX mode is proportionately larger.
No matter what the manufacturers imply, the megapixel count has zero effect on picture quality.
The camera's sensor is more important than its megapixel count.
A high megapixel count and compressed files will help ensure that you'll be ready when you see something worth shooting.
This in turn allows cameras using the sensor to achieve a higher resolution with the same megapixel count.
And yes, of course there are other important things in a camera, and the megapixel count has been over-used as a selling point to the naive.
Low light photography is much improved over the G10 thanks to Canon correctly lowering the megapixel count.
For instance, a camera may capture a one-megapixel image but claim a 1.4 interpolated megapixel count.
High megapixel counts are primarily related to printing, which requires much higher dot density.
Another example is the megapixel count of a digital camera.