"We Don't Bet Each Other on the River..."

[W. Deranged]

So I play in a live 10/20 "private" game which has a whole bunch of regulars. Everyone's played with everyone before, and I'm kind of the "new guy." (Not to mention many of the other players are old and I'm a college kid and so on and so forth...)

Many of the players, though, have weird arrangements where they don't bet at each other on the river. Some arrangements even involve giving certain opponents their river bets back if they called in a multiway pot and their compatriot won, or even basically shutting down the betting (and sometimes actually exposing their hands) as early as the turn. Players comment "I'm checking the turn with Aces" or "I'm on a draw" all the time when they are in pots with "friends." It is really, really strange. I once even saw a guy preemptively turn over his hand on the turn against another player who was not aware that such an agreement even existed. The player graciously stopped betting, but I would have been upset in his situation.

Now, this doesn't directly effect me because this doesn't happen in hands I'm involved in, but I was just wondering if others had seen similar behavior in live games in the past. What is deal? Why do people do this? Is this some sort of well-established poker courtesy or something?

I know when I play against my friends I play especially tough and especially tricky because we respect each other and want to demonstrate our best play.