You're right, I was coming at this from the news/documentary side of things. If Moore's movie were classified as commercial speech, he might be vulnerable.

I have a hard time seeing that happening, though. He's not selling anything except his movie, which obeys the form of documentary. I have no idea if there's a legal definition of "documentary", but I'd bet it's pretty broad. Courts tend to be reluctant to limit expression, and err on the side of permitting more rather than permitting less.