You are confused between the number of pixels in the file that the camera makes and the number of pixels that the printer needs to print.
To get a decent picture the printer needs to print at least 200 pixels per inch. Thus a decent 8 x 10 picture would be 1600 x 2000. I prefer to get 250 pixels per inch for the print, thus a final picture of at least 2000 x 2500.
Ok, well you say, then I do not need the 2000 x 3000 that the camera takes. This would be true if you used the whole frame to print, but usually you crop the frame in photoshop or some graphic program and so you start with a 2000 x 3000, but dont use all the pixels when you crop and wind up with a lot less than that. Say you try to blow up (crop) a head out of the center of a picture,--even in a 2000 x 3000 pixel file, you might be down to 800 x 1000 pixels by the time you get through. That would only be 100 pixels per inch when you output 8 x 10 to the printer. You would see big square pixels on the paper.
Secondly, on the file size, I have played with the D-100 now for about three weeks, and have tried all modes. The ONLY MODE to shoot in to get the best picture is RAW mode. The files are much larger, but that is not because there are more pixels, but because JPEG throws away a lot of the information which the picture takes to compress the file. JPEG is an 8 bit file format, whereas the RAW (NEF) files are 12 bit in each channel.