This seems to be popping up a lot lately. Here's my experience...
I used the Mears shuttle last Sept...staying at the Swan. When I asked the 'not so nice' lady working the Mears area why they didn't just put me on the bus heading to YC/BC, BW since it sometimes stopped at S/D, her response was, and I quote...."DME is for those staying at a Disney owned resort. The S/D are not owned by Disney, you have to take Mears. You won't get on a DME bus!!"
But, there is signage for the S/D at DME. Why? Because the S/D are
Disney cruise pickup and drop off spots. So, if someone books a land/sea pkg for a Disney cruise, one of the bus stops will be the S/D. Those are the guests that get to use the DME to those two resorts...no one else.