Let's start with the facts. Here's the spec. It's called Encrypted Media Extensions (EME).
https://dvcs.w3.org/hg/html-media/raw-file/tip/encrypted-med...
The EME spec isn't that long, and the introduction has a nice diagram. Go check it out.
The W3C spec does not put "DRM in browsers." It allows browsers to use "decryption modules" that already exist elsewhere, like in the OS platform. There are APIs to determine what sorts of "decryption modules" are available and to use them to decrypt media.
If we're going to transition to a plug-in free web then we need HTML5 video to support these extensions. Sure, it'd be nice if the big media companies stopped insisting on using encryption to distribute their videos. But that's not likely to happen anytime soon. Premium video on the web requires either plug-ins or EME. I think most of us would pick premium web video + EME, rather than premium web video + plug-ins, or (perish the thought) no premium video on the web at all.
BTW, open source browsers can easily implement this spec since it doesn't require the browser to implement a "decryption module" themselves. Also, there is a mode called "clear key" that can be used if the underlying platform doesn't have any "decryption module" available.
Disclosure: I work at Netflix on streaming video in browsers.