Airbnb expanded their offering to hotels (including boutiques and bed and breakfasts). According to them, they're seeing strong growth in this segment[0], which is probably related to your hypothesis: there's a group who aren't comfortable with the home-sharing model (or people who simply like hotels) and they're finding ways to serve those people.
The HotelTonight acquisition seems like it's a way to more rapidly scale their hotel inventory than anything else, although I suppose last-minute travel may simply be better served by hotels than home-sharing.