I agree with you and think that especially if you truly enjoy wine, the wine you serve at your wedding will be important to you.
I think that bringing this up to the BM is important and explaining to her that you were led to believe something else about your wine choices when you booked. I'd wonder if this is a new policy too.
I think its reasonable for them to purchase wine that is to your liking. You've got me a bit thinking about the same thing for my venue....