It's been a running joke with my friends for years that none of us give the slightest fuck about our W/L in CoD because you are constantly being put into games most of the way in progress, and guess what, if you're joining a match in progress most of the time it's because someone quit because their team was getting wrecked so you're joining 30 seconds before the matches ending and you're losing 2:1!
So while you shouldn't really care about your W/L generally speaking, for any sort of stat tracking it kinda fucks that and instead has people place emphasis on K/D, which is about the only thing most people care about in CoD, which leads to what could be considered "bad" team playstyles. Most people don't care about winning partially because of this, which is why you see tons of people just camping and/or whoring their K/D and ignoring objectives, etc. This happens in all games, but this happens in my experience drastically more in CoD then Halo, and I'd attribute it largely to that. I don't really have a problem with join in progress since I hate my team quitting and me being forced to finish out a match where I'm outnumbered 6:1 and there's five minutes left on the clock, but there's a flipside to that too.