The reason why you don't press "Surrender" is that many times a player will have been beaten, but his team will still have a chance to win. By pressing "Surrender" the replacement AI does nothing at all. It won't make new ships or move its current ships. A beaten AI isn't much help, but if it can make ships and serve as a thin meat shield, at least that's better than nothing. Also, many players just feel that they haven't personally been beaten when their allies were responsible for losing the game. For those reasons people just press Quit and not Surrender.
The way to properly read people's record is this:
Wins = Wins x Completion Factor
Losses = (Games Played - Wins) x Completion Factor
The Completion Factor is that portion of games that end up being legitimate--games without early minidumps by someone. If an ally minidumps out of the game 5 minutes in and everyone quits to remake the game, it's really neither a win nor a loss. I figure that the actual Completion Factor is about 90%.