I do agree resetting the ratings at every update is a big hassle. I wonder why Apple doesn't have the reviewer determine whether or not the rating should be reset. Perhaps that would introduce too much power to the reviewer(s?).

Every update may be a bit excessive, but it's better than never. A review is made at a point in time and a product can get better or worse over time. If I ever get begged for stars though the app gets one star.