While the Developer Subsidy at SSR is truly in place, it's worth noting that in 2006 the subsidy is only 0.0768 per point. Add that to the $3.98 that members are paying, and the dues would still be lower than OKW.
I think it's a combination of the resort being newer, the rooms being smaller than OKW (may seem like a minor thing but it does equate to lower quantities of everything from furniture to carpeting to roofing materials) and finally the fact that SSR is significantly larger than OKW. Expenses like the front desk staff, bell services, gift shop, etc. are spread over more members, meaning each member pays a smaller portion.
Even for something like park transportation (which is a BIG expense), until SSR grows to the point that they need to add EXTRA busses due to vehicles reaching capacity you've got the same expense spread over more members. If their goal is to run a bus every 15 minutes to each destination, I suspect you can pretty nearly service 800 units with the same bus frequency as you can 500 units. If that's true, you've got a lot more members sharing in the costs.