These lending sites are a disguise for scammers. The community where you can ask for a loan is not very much different from your circle of close friends where you can ask for a fiat loan as well. But that doesn't somehow make banks obsolete. A real Bitcoin bank will require you, as a borrower, to provide liquid collateral, and I don't think that they are going to consider altcoins as one such. In this way, they would protect the bitcoins they themselves might receive to deposits from Bitcoin users...
Personally, I think it is only a matter of time till real banks start offering Bitcoin related services (e.g. deposits and loans)
Banks don't need deposits to give out loans. But that wouldn't work with Bitcoin