Yesterday the average rating of all plugins on the wordpress.org repository changed; ratings that were not linked to a review, were removed. That means that ratings dating from before approximately November 2012, when reviews were introduced, are not being taken into account any more.
This had a positive impact on the average rating of my own plugins, but especially so for Autoptimize. That plugin was largely unsupported before I took over in January 2013 and got some low ratings as a consequence (the average was 4.2 at the time, if I’m not mistaking). With those old numbers now out of the way, the average went from 4.6 to 4.8 overnight. Yay!
[Update: a couple of days later there were even more changes on the WordPress Plugin pages.]