Absolutely, I have thought about that also. Many raters will leave the star on whatever it was last on... so, if your level gets 5 star rated and enough people leave it at that 5 star it gets harder and harder for it to drop to 4 stars. Same with 4 stars.
But since people generally leave it at the rating it originally was at, that means a 4 star level will slowly keep slipping, while a level that is cemented pretty well at 5 star will continue to be at the top of the heap. I've been watching this for a number of months.
Splat Invaders Saga used to be on page 3 of highest rated - but since virtually everyone leaves it at 4 stars it slowly slips down - now at page 30 of highest rated (where you can hear the crickets chirping).
I've seen a lot more movement down with 4 star rated levels, however the 5 star rated ones get cemented there and rarely go down.

