You know, I never really thought about it that way. Letting your opponent get an EM doesn't make you lose any more electrum.
I don't play PvP very much. I almost always lose. What I don't like is the fact that it takes about 10 seconds for the computer to process your turn and send it to the opponent. It's not that your opponent is thinking. The card that the opponent draws doesn't show up until after 10 seconds.
10 seconds may not seem like much, but when it happens every turn, especially in a long game, it makes the game a nightmare. I soon realize that I could be grinding 3 AI3's in this amount of time. I finish the game, and stop playing PvP.
As for my views on quitting, I think it's not polite. At least let your opponent have the experience of playing a human for the rest of the game. It doesn't take very long, and it makes you seem more cultured. I've never had anyone quit on me, and hopefully I never will.