Note anymore, the rank system is actually pretty deep, and is based on your stats (even more than just what shows is post game) That way, no matter how many you win, you're rank is really how well you play. They took the trueskill system and modified it. They used to have a good thread on the bungie forums explaining it... now I forget where it is. ah well.

Edit: did a little more searching, they take all of your stats and do comparisons to the people of the same level, and that track how consistent you are with those stats. That is also how they judge your trueskill rank. However, wins do count towards your trueskill point total, as well as how high you finish on your team.