When we stayed at ASMo the second week of June last year, the busses usually stopped at all 3 All-stars with movies being the last stop. We always went to the parks at opening and left at closing and never had a bus just for the ASMo. I am sure that during peak periods such as Easter and Christmas/New Years, they each have their own busses, but we were there when it was fairly busy and we never experienced this. That being said, we never had a problem with busses at the resort, and the only place we experienced significant waits was at Downtown Disney.