While its nice to have the image quality produced by 'proper' SLR camera's. you do run the very real possibility of destroying some very expensive gear. I've seen SLR camera bodies and lenses that have been merely splashed with salt water and they are completely stuffed. Unrepairable. They have as many delicate computer bits on board as your laptop PC. Would you stand in the surf holding your laptop?
There are no waterproof SLR's that I'm aware of. Yes you can buy sealed perspex housings for them (these are what surfing photographers use) but they are very expensive, often as much as the camera itself.
The upside to this is that compact waterproof cameras are getting better as to image quality and usability.
Many still suffer from the horrible electronic viewfinders (like a video camera) instead of the optically better view through-the-lens that you get from an SLR.
That aside, the image quality, (if the camera is used properly) is very good.
Most people just want a snap of someone holding a fish, or a snap of the beach itself. Hardly challenging photography. Most waterproof compacts could do that with relative ease.