Image size and resolution are not necissarily related.

A film speed of ISO 100 is a high resolution film and will reproduce a quality print. ISO 400 is a high speed film that will produce a lessor quailty low resolution print.

Digital cameras mimmick film in that 10 megapixel is a higher resolution than a 2MP, you want the 10MP for image quality.

As for digital resolution, the best way to describe is-

Two monitors, a 18" widescreen and a 42" widescreen, if the resolution of each monitor is the same the same image will appear in like quality with only one difference, size.

When you resize your are changing the image size and not the resolution. As for the 2MP image being a smaller file size, yes of coarse as it contains LESS information or in other words LESS resolution which translates to GRAIN. Again to relate this to film, there is less information in one exposure of 400 film than the same exposure of 100 film. In the case with the Nikon packing such a large files size, simply higher resolution which is more information which is a high quality image.

Scott