The purpose of DME is to transport guests...not luggage. The luggage delivery service is a perk of using DME.
So, with that in mind, you got very lucky that you were allowed to just walk up and get on a bus. The private car service people and cab owners put up quite a stink when DME came into MCO. The only way they were appeased was Disney promising the airport that they would accept no walkups at the counter. You are supposed to make a prior reservation. You can do it the day before, but it has to be in their system when you show up at the counter.