I agree that a player should only be excused from a game in progress with the consent of the group he's playing with, or get a WD (withdrew) posted on his/her stat sheets (so that future potential playing partners can check out the likelihood of any new partners going AWOL.
As for a single player just knocking in a round by themselves, I think it should be up to them to determine whether to quit or continue. There are too many reasonable causes for quitting on a round for the casual player that is dependent on their computer equipment, how well their browser is functioning moment-by-moment, their LAN router, and the speed and reliability of their internet connection: swing meter jumpiness, frequent excessive load times and freezes, how well the WGT load manager is doing on any given day, etc. Family craziness (for those of us with full households and no cave to hide in), also effects play, etc. Stuff no player should be penalized for who is just trying to get some ranked time in. No one gets rewarded excessively for merely lowering their scoring average. For those that really abuse the scoring system, wouldn't an artificially low average only hurt their chances against honest handicap players (as in real golf)?
But I absolutely agree that abandoning a group round during an agreed upon match after it has begun is really a crappy thing to do. If WGT registers these matches, why couldn't it post a WD on the offending player's stat sheet?