[mousepod]

If I remember correctly, Michael wasn't saying that Walt was at his most popular, but that when he originally started his company, he started it as an artist (as opposed to as a businessman), and his audience rewarded him for being an artist. In his book, Barrier talks about Snow White being an artistic peak for him. According to Barrier, Walt never was able to reach the height with his animated movies that he had in his early pre-war years. By the mid-'50s to early '60s, Barrier talks about Disney throwing himself into other, non-theatrical projects, such as Disneyland (the TV show and the park). Knowing that his studio was basically churning out mediocre feature films, Disney struck out again as an artist in other forms and was rewarded by his audience for it.
(sorry if that answer is articulated poorly - I'm kind of burned out right now...)