Netflix creates tons of original content so it is both a producer and distributor. If Netflix really believed that the marginal value of DRM was zero they wouldn't use it on their own content since it has a nonzero cost on the distribution side.
The only other possibility that I can come up with is if Netflix's original content has multi-party rightsholder situations with contacts that legally require them to apply DRM even to "their own" content (IANAL and don't know much about how these things work, but it wouldn't surprise me).
