O-ring once bubbled...
"You see, diving is not important at all..it is the photography that is important. Scuba is just a means to an end...namely, getting the underwater shot. I don't like to dive, am a horrible buddy, and am only interested in viewing the underwater world through a lens. I spend more time with my camera equipment than I do my dive gear and I could care less about the sensation of being underwater."
There's two distinct differences in underwater photographers.
1. Divers who photograph. Taking pictures is secondary to safety, good diving practices, and ecology.
2. Photographers who dive. Getting the shot is all that counts. See the quote above.
We've all seen good examples of both.