Not much I assume. The average buyer doesnt get any of it. 
First of all the child would need to have a specific need regarding a theme that cant be fulfilled by stores. 
Second, the parents need to care about fulfilling that need by ordering stuff through DS which is a bit harder than just walking into a store and getting it there, unless no stores are near. 
Here in the Netherlands I am not familiar with that concept since you can pretty much buy playmobil everywhere there are stores. I live in a larger village and we already have two places where its sold, with probably about twenty more stores half an hour away in the nearby cities and villages. All toystores have it, and any other store with a toy department has it as well. 
Though I gues that unlike the stuff from stores, the DS stuff is probably bought far more by collectors than anyone else. I'd gues 3/4 of the DS orders might be from collectors, or at the very least half of it considering the quantities that stuff is often purchased in.