Stupid thought, especially thinking about Netflix's history as one of the earliest services that streamed licensed content, it would not surprise me if this was at some point a way to minimize how much unencrypted data was in memory or similar.

Other thought would be, whether the architecture was somehow related to how one had to do things in Silverlight (any silverlight devs still remember how one would do this sort of thing? Any Silverlight devs still around?)