Not to get caught in the middle, but I use "thanks in advance" all the time to sincerely thank someone for doing me a favor that I'm asking, and not because I'm assuming some kind of dominance over someone I hold to be my inferior. I sure hope that my way of regarding the term is the norm. This is the first I've heard of anyone considering it to be otherwise. That said, people in my family used to say "bless your heart" and mean that as a sincere compliment, so it was some time before I learned that it was a way of telling someone that they're stupid.