Taken from howstuffworks:
A 2.1-megapixel camera can produce images with a resolution of 1600x1200, or 1,920,000 pixels. But "2.1 megapixel" means there should be at least 2,100,000 pixels.
This isn't an error from rounding off or binary mathematical trickery. There is a real discrepancy between these numbers because the CCD has to include circuitry for the ADC to measure the charge. This circuitry is dyed black so that it doesn't absorb light and distort the image.
So I assume 4 megapixel would be similar, only at a different ratio
2272 x 1704 seems to be the maximum a 4 mega pixel can MAKE, I would assume that would also be great quality otherwise the camera wouldn't have the function to make the resolution that large