These people do know about camera angles, but the whole point of this website is to point out things like this. They're not getting at the camera man or anything, just saying that it happened.
It's been said pretty well: "Everyone knows it's a TV show". Exactly. It's a TV show that we watch, but no one on the show ever comes out and says "Hi, I'm David Schwimmer, and you are watching a TV show. My name is not really Ross Geller." In the same vain, although almost everyone with a brian is fully aware that Friends is a TV show filmed with TV cameras and stage lights to light the set, the viewer is not supposed to actually *see* the apparatus in accordance of the whole "suspension of disbelief" idea. Get it? It's a slipup, because you're not supposed to see 'behind the scenes.'
Chris and Prozacfairy - what on earth are you doing looking at this site, if your answer is 'it's only a tv show'? We know that!! The same type of comment could be made about any slip-up in the whole archive. The fun is in finding slip-ups and commenting on them.