If you check out other cartoons from the 1980s and early 1990s on Wikipedia, it seems that most cartoons show their new episodes during September-December. This is guessing on my part, but the reason I think they wanted to release a cluster of new episodes is to immediately capture the attention of children for merchandising profit for the December holiday season.
With the 2K3 and 2012 versions, it seems that they are spreading the episdoes throughout a typical TV show's season (September-May). I don't know the exact reason as to why most cartoons have gone to the traditional TV schedule, but I'm pretty sure that the internet (kids can now easily check out TV listings online rather than in the past, depending on their parent's TV guide or randomly hoping for a new episode; also the shows could be viewed online during their airings) and the
Children's Television Act probably influenced this new airing schedule.