Well, a lot of people come here to learn, and I would suggest that maybe there are many instructors for the following reasons...
1) they enjoy teaching, so why not on the net as well
2) they are hardcore about diving, so if they aren't wet, they may as well be thinking about it
3) they realize that they can learn from others, just as much as others can learn from them
I really appreciate all of the instructors on the board. I know that when I did my cert a short time ago, I discussed gear and things with the instructors, because I thought that these people work with the stuff on a regular basis, they will use lots of it, and will want what works for them.