The marketing of both resorts tries VERY hard to NOT differentiate themselves from all the other disney resorts.
While the DDP is certainly not a drawback for some, I would bet a lot of people book through disney and then want to add the DDP only to find out it's not possible. If you look at their website, they even use the same language like "counter service" in the drop down lists. This can be very deceiving to people that aren't reading the "fine print".
There are plenty of very good reasons to stay at the swan/dolphin but if the DDP or being able to charge to your room at disney are deal breakers for you- then it's good to know ahead of time.