If I were to picture Arthur's animation to change, I would have thought Between the Lions shorts. But I'm glad that they didn't go in that direction.

I assumed that Arthur would stop with at most six seasons because usually PBS's animated series last no longer than that while the live action ones (Sesame Street, Mister Rogers' Neighborhood, Reading Rainbow) last for decades.

There are two animated kids' shows that I know of that have ran for almost as long as Arthur: SpongeBob SquarePants and Pokemon. I don't know whether the original viewers of those shows are getting tired of them or not.

Spongebob aired it's first episode back on May 1st, 1999. Pokemon aired it's first episode on April 9th, 1997. Arthur aired it's first episode on September 2nd, 1996. Arthur is older then both of those shows, but Pokemon has more episodes then both shows combined. However I can say that Pokemon and Spongebob both have declined in quality of episodes.