It sounds like travelers to Vegas, the hotel capitol of the US, are savvy enough to check airbnb. And VRBO it seems as well. This is a big pain for searchers. Hipmunk shows each of these, but not very well as they only have a handful of the 1000s of listings from Airbnb. We've tried to help with this at http://AllTheRooms.com by aggregating everything we can find.