Though they are planning to launch additional services [2] @aaronapple below (above?) is right... regulatory changes are on the way.
Right now they're violating the law, don't collect or pay local taxes unlike real hotels, don't bother with ensuring that local rules and regulations are followed.
This will (and should) change soon. Hiding behind the people who rent out their spaces who are "supposed to pay local taxes" won't hold. Customer databases will need to be released to the IRS or local taxes withheld (which [2] indicates they're working on already).
Once they are forced to play on a level playing field, their rates won't be as competitive and their service not as popular.
[1] http://qz.com/190432/airbnb-doesnt-even-own-a-bed-but-its-ba...
[2] http://www.fastcompany.com/3027107/punk-meet-rock-airbnb-bri...