I had someone concede, before losing. Is the prizes better, if I concede?
It comes down to time, mostly. A lot of players feel that they’re wasting their time playing out a game they can’t win. Your XP for just playing is 400 per hour in Ranked and 300 per hour in other PvP with a bonus for winning and a penalty for losing (I was unable to find out exactly what those are, though), but still, some people want to move on to the next game.
I believe that in this case your MMR doesn’t decay and the next opponent will be as strong as this one.