While they generally stay the same from day to day, DME bus routes can (and do) change on a daily basis (and possibly even *during* the day) based on expected crowd levels (which is one reason why they ask people for their flight arrival info).
But each DME bus will stop at a maximum of four hotels. And I believe the order of the stops is left up to the discretion of the bus driver.
-Rob
Yes ... all of what I quoted above is accurate.
WDW resorts are divided up into roughly geographic zones, but these aren't adhered to at all times ... if it will be mor efficient to group guests on a bus that crosses two or more zones, Disney will do it that way. Because you need to make a reservation for DME, they know roughly how many people are going to which resorts and at what times, and therefore they can group and dispatch buses that way.
For the record, all three All Stars resorts are in the AK (Animal Kingdom) DME zone, along with Animal Kingdom Lodge, Animal Kingdom Villas, Coronado Springs Resort and Pop Century. As you can see, there are 7 resorts in the AK zone, and there will be no more than 4 resorts grouped into any single bus. When a bus will cross two or more zones, they will group a maximum of only three resorts onto that bus, to make up for the increased travel time.
Also, for the record, when I stayed at Caribbean Beach Resort, which is in DME's EC (Epcot) zone, my bus dropped off guests at CBR and then AK and finally All Star Movies. Obviously, that bus crossed zones, and as you can see, the bus had three resorts rather than 4. Those numbers, the number of resorts per bus, is a MAXIMUM. On my other 2 DME trips, both of which stayed within one zone, I also had only 3 resorts per bus.