I have thought about ratings by page views but once a map gets to the top it is unlikely to ever leave. The problem being that people really do listen to rating, back when I first added ratings the number one viewed map went from Africa Challenge to BC Gold, which is good. Counting by downloads is not much better and would also require adding download tracking.

The current format comes down to if someone wants to recommend a map. At some point in time I will likely have to rejig it to be more obvious which maps are highly rated.
This system is not that much different from pageviews/downloads, the difference being that it is more directly tied to the quality.
It has everything to do with the fact that a download/pageview says nothing about the quality of the map.