Not quite. The resolution of the file is the same whether you use Superfine or Fine mode. But more detail will be preserved in Superfine. JPEG compression works by discarding details to create contiguous areas of colour as these can more easily be compressed. It's easy to see if you save the original RAW (if your camera supports it) as a TIFF, then save a 10% quality JPEG and compare the two for fine detail (for ex&le hairs, texture of cloth, pores on skin).
So why do people willingly throw away detail? Well, if you're resizing to 640x480 and people are looking at your image on a 72 dpi monitor, they aren't going to see your detail anyway. Always capture the best quality you can if you intend to print.
