Ok. Here's my two cents and how i see it.
1) He doesn't care about the wedding, he cares about the sex afterward.
She cares about the wedding, and is anxious to get everything ready early so there are no mix ups later.
2) Yes, she MAY be in control of the relationship. In other words, he's whipped, he'll do anything she says because he is insecure or for whatever reason there may be.
3) He might not have someone to pick for the best man.
I think you should let HIM know how you feel IN PRIVATE, without his fiancee around to sway his response. That way, he'll give you a straight answer.
Tell him that you feel the best man is too much of a responsibility for someone who is not as close to him as others, such as his brother or a best friend.
Ask him if there is anyone he might have in mind to replace you.
Ask him who his CLOSEST friend is, and then ask him why that person can't be the best man.
If they both insist that you be the best man, then go speak to the bride IN PRIVATE next. Tell HER how you feel about the situation. Tell her that it should be the groom's decision, and (if you are comfortable enough to discuss this) add in that if she continues making decisions for him, he will begin to build resentment early on, even if he doesn't show it or says "i don't really care." Because inside I am sure he does care, and he's just letting it go to make her happy. That won't last forever. And it's bad for the relationship (speaking from experience here).
If they STILL insist, then suggest that the groom get to choose the bridesmaid out of one of his friends, WITHOUT the brides influence on his decision.
Sorry for the wall of text, this guy just sounds a lot like me. Shane02pro5 there has a strong point, and I agree with it. He seems to be laid back, and he loves her, and doesn't like conflict. He just lets things go even if they bother him inside in order to avoid an argument. She can be a very good arguer, which could exacerbate the situation, causing him to avoid more conflict. Again, speaking from experience. I'm telling you, it may even be better for them to get into a fight now, because if he holds it in, it might come out years from now.
Ex. "You won't let me go to the Mets game!? What the #$^%! You never let me do anything! You didn't even let me choose my own $%#^@ best man! I'll NEVER get to do that again!" .........you get the idea.