It's standard practice at both Cartoon Network and Disney to kill a show after reaching 65 episodes. I've read about this before with people disappointed about various series being cancelled.
This practice ties back to the days when local stations aired cartoons in the after school hours during the week. Sixty-five episodes allows a station to strip the show (air each day during the week at the same time) for thirteen weeks. After that time, they would swap in another show, and do the same.
That way they can use four shows in the same time period throughout the year.
I don't know how valid this practice is these days. I can't remember the last time I saw a cartoon on the local stations in Chicago during the 3 - 5 P.M. timeframe.