Hm, I don't really think of it quite in that way. Both of us are extreme introverts, so going out we consider to be work. It takes effort, it makes us tired. By the time we were seeing each other more often (ie, him staying over the weekend), we had gotten comfortable enough with each other, that we didn't have to worry about impressing the other person, which is what you kind of do when you "go out" with someone. And if you're only seeing someone for a few hours at a time, there's a bit of implicit pressure to make sure they have a good time. Which, with him, is a fool's errand. Nobody can make sure he has fun. The only thing I can do is make sure he isn't particularly miserable in a social situation.
I think if one of us was a lot more extroverted, it certainly wouldn't have felt as comfortable as our relationship has been. I sometimes go out with my friends without him, but it certainly isn't an everyday thing, or even an every-week thing. I think if one person feels the need to go out every night, while the other person likes to stay home instead, there might be some friction.