IIRC everything except Edge and Safari are forced to use Silverlight for Netflix streaming. I'm not exactly sure why this is, but it probably has something to do with the mess that is video codec licensing.
It's not necessarily DRM in HTML5 which is the issue here although I suppose the fractured nature of it may be partially to blame. It's the fact that it's seemingly arbitrary that Chrome gets capped to 720p and no one knows why. Did Microsoft pay a big chunk of change to Netflix for exclusivity or something along those lines? Do the content creators prefer Microsoft's DRM implementation over Widevine's?