Because the S/D are not owned by Disney, they aren't allowed to participate in some of the perks the other, Disney owned, resorts can. Such as....DME and the dining plan, free or paid for, or charging back to your room in the parks.
But, I love the Dolphin. If I can get a good rate there, that's where I like to go if no DVC villas are available!!!
They are more of a deluxe resort vs a moderate. Actually tend to be more deluxe than the Disney deluxes in my opinion!!!