Really interesting topic. I've thougth about this a lot, especially since I was first exposed to "Curb Your Enthusiasm," which has no laugh track. I think the issue is comfort. When there is a laugh track, you feel more comfotably laughing, because you hear others laughing. It's just group mentality. Though you would find it just as funny without the laugh track, you're more likely to laugh out loud with the laugh track. It's the same thing with watching a comedy with friends as opposed to watching it alone. Personally, I laugh more when I watch it with friends, just because they're laughing too, and I get more caught up in the humor.
I often feel more comfortable watching a show with a laugh track, for those reasons, but you're right -- when I stop to think about it, it seems really strange.