I'm not sure about the moat either. While planning a trip recently, I checked out Airbnb, Booking.com, VRBO and Homeaway.com for the same area. I found that Booking.com and Homeaway.com both had some of the same listings. So landlords are certainly trying to bypass the moat. (Homeaway.com is in fact co-hosting Airbnb listings through a partnership, but they're also apparently transitioning away from that to become a full-blown Airbnb competitor.)

I suspect the moat won't matter that much, since a consumer ultimately doesn't care about which service they end up booking with, as long as it seems trustworthy, and landlords have little reason to be loyal to one service when there's no downside to being non-exclusive.