Is it normal to rely on the same, small group?

I hang around pretty much exclusively with a very closely-knit group. My room-mate from college, his sister, her friend, and then a couple of people we picked up along the way. Some of us have dated, some are related, and although we occasionally find relationships outside the group, we don't let those people into the group.

We see each other pretty much every day and usually just hang at one of the two apartments that four of us live in.

I think I rely on them because I'm the kind of guy who finds it difficult to mix and who makes jokes all the time, even in my small group. As for the others, I don't know why they're so hooked into this dynamic we have. It's not like any of us really have much in common. The other five comprise an academic, an actor, a chef, a waitress, and a masseuse. We always seem to find something to talk about over coffee, though.

Is this scenario normal?