It's a different target demographic. In a trip to DC recently, we got a private room on AirBnB and saved roughly $25 pr. night ($75 vs. $100) over the hotel we'd otherwise have used, and we got a better experience for it.

We didn't feel any obligation to hang out with the host, bring gifts or stay in touch, or to accommodate our host or anyone else at our home -- which made things a lot easier.

I think it's more correct to think of AirBnB as cheap hotel, not premium couchsurfing.