As far as surprising places where AirBnB is hard to book - I'm surprised Boulder, CO isn't on the list. For as tech-heavy their city is, I recently went for a short consultancy there with a startup and found it nearly impossible to find any airbnbs anywhere. I think there were 3 with some availability in the whole city.
Moreover, hosts told us that there have been recent regulatory changes and new registration requirements which seem to have had the effect of limiting supply.
To my surprise, AirBnB is very eager to send refunds for bad experience, instead of concentrating on removing the bad hosts and guaranteeing a minimum level of quality. I really hope that they will work harder on this, because if a first-time user tries their service in SE Asia, chances are that he or she will never consider them again. Booking and the like are far more reliable in that region.
I suspect they think it might be community-unfriendly and/or complicate the service.