Netflix wants to switch not because they're looking for DRM. They want to switch because they're looking for a better platform that also supports adequate DRM. Sure, no matter what they come up with, somebody's going to find a way to circumvent it. But the majority of people aren't going to put that amount of effort into it.
Besides, from all signs, not even Microsoft takes Silverlight seriously anymore. ( http://www.infoworld.com/t/microsoft-windows/microsoft-shuns-its-own-silverlight-while-embracing-flash-214335 )
Switching to HTML5 will allow them to build a user interface that will work on any system that'll run a modern web browser and stream video content as long as a supported DRM module is available.THAT is the reason that, as of now, the only way to stream content from Netflix on linux involves using WINE. They climbed into bed with Microsoft and moved their platform to be 100% Silverlight, and Microsoft absolutely refuses to allow their DRM interface to be ported to Mono, which means that any system that isn't Windows or MacOS is SOL.
DRM support in HTML5 allows Netflix to be in control of which platforms are going to be able to play their content.