This is probably one for Airbnb themselves but if a guest doesn't leave a review does it affect the hosts actual rating? I believe that if either host or guest doesn't post a review then neither should be published. If it does affect the host rating then this is totally unfair and dicriminatory.
I recently had a couple stay and they recieved excellent hosting including chocolates for the lady as it was her birthday and two Gin & Tonics, print outs of walks in the area, a restaurant booking that they loved and a cooked breakfast the like of which they have never experienced before (in a good way). Leaving and assuring me of a 5 star review as nothing could possibly be improved upon no review has been left. Even after they left a pair of leather gloves that I posted back to then by recorded delivery, not even a thankyou.
Sorry Airbnb but it's not satisfactory.