While I do enjoy playing Magic The Gathering on my iPad and PS3, it seems good sportsmanship exhibited by other players rarely exists. I'd estimate that in 80-90% of the multiplayer games I'm in where it's obvious I will win the match, the other player will exit the game which causes a slow down waiting for the computer to take over for them.
I'm not sure where the lack of sportsmanship comes from. Anytime I know I'm going to lose, I give my opponent the satisfaction of finishing me off and completing the game. It's a real shame the game doesn't punish those who quit out.
Even worse than people who "quit out" is people who will take the maximum time for every move they make likely in an attempt to get you to quit once you lose patience. Magic 2015 definitely gives players way too much time to make moves.
Perhaps the anonymous nature of online interaction encourages rudeness...who knows...