I can't imagine why that'd be. I seem to remember that most newspapers use the term "Michiganian." And it sounds more official, more conservative, doesn't it? (By the way, I've never in my life heard of a "Michiganite," which Webster's lists.) If there are any lexicographers out there in the TOSC readership, lemme know.
This will now, of course, force me to do some deep soul-searching about who I am and what I call myself. I've always insisted on the "Michigander" label; the word's slight gawkiness and what I assumed to be alternative nature held much more appeal to me. Jim Blanchard is a Michiganian; I'm a Michigander. Or am I? Now that my two main dictionaries have spoken, do I attempt another verbal flipping of the bird at The Man by going with "Michiganian"? Or by doing that am I falling right into The Man's hands? By slavishly rebelling against the dictionaries' proscriptions, am I in fact giving The Man even more power?
My guess is I'll stick with "Michigander." For one thing, it's what I'm used to. For another, I feel it allows me to better show off my nasally dominated Upper Midwestern accent. To sound like me, you've gotta hit a hard, hard "a." None of that soft-vowel crap that Californians like to pull.
And, anyway, that's what the dictionaries would have me say.