> Personally I don't care if there is no incentive to go above and beyond the base level of service. All I want and expect is the base level of service.
This is the exact problem. A base level of service should be three stars, but people have been conditioned to read five stars as base level, and anything below as problematic. The whole point of a rating system is to get an idea of what to expect. When different people rate on different metrics, the data doesn't actually represent what you think it does (whichever metric you subscribe to).
The only reason anything less than five stars is interpreted weirdly is because people started rating weirdly and then start taking that into consideration when looking at the ratings, and it gets all confused. Many of these ratings systems clearly state what each rating level means, and people still don't rate by those criteria. People have been culturally indoctrinated to rate things incorrectly (that is, they specifically don't follow the instructions in lieu of following what has become the norm). This compresses one end of the spectrum which leads to loss of fidelity on that end. It's clearly worse than a system where people actually followed the criteria and we could actually identify a five star average as exceptional, a four star as good, and a three star as sufficient.