The issue is light. Today's digital camera are not suitable for most underwater light levels. Give it a few more years or carry a lot of lighting.
When can we expect 12 to 15 megapixels, 10 to 1 zoom digital cameras to hit the market? Those of us who are into underwater photography (with a housing, of course) need the increased resolution such that when we do a heavy crop, we still have 5 to 8 megapixels available for enlargements.