They wanted the artic Xcelsiors in Brooklyn when they were doing the B38 and B1 conversions since the Xcelsior is already in Brooklyn and no new orders were delivered.
Most people are probably just taking the B6. The 6 has the benefit of bringing people to the IRT where as the 82 is just the Broadway and 6th ave lines (both suck ass during the weekend compared to the IRT)
I wouldn't be too quick to ax the B63 overnight since that is the only N/S (or w/e it would be considered as ) route for many of the places it serves at that hour.
It happens but not as much as the local bus. Some drivers just don't want to be bothered. I had a kid try to board a BM1 using the old school "can I can a ride", and the driver wasn't having it.