The web would certainly be better off without Microsoft Silverlight and Adobe Flash Player, but the idea that putting DRM into HTML itself to make them obsolete is absurd. The EME proposal would not make proprietary, platform-specific plugins disappear; in fact it makes a new space for them as Content Decryption Modules (CDMs). These would be no less of a problem for Web users, especially those using free/libre and open source browsers and operating systems. The fact that they would gain legitimacy as a Web standard would make them a much bigger problem.
Just one of two other great points about DRM in HTML5. Want to watch Netflix? Well, your browser provider will need to sell their soul (and you can buy it back provided you download this CDM and pay $9/mo for the rest of your life).