Except that the Web's getting DRM exactly so that Hollywood can restrict content to proprietary platforms that allow DRM. Right now, the main use for HTML5's DRM support is DRM on Chromebooks - hardware that's only available from a handful of approved suppliers and is locked down from the hardware up to stop the user running any non-manufacturer-approved code on it. If you enable the ability to run your own code, the DRM module refuses to decrypt anything, and so far as I know no-one has found a way to bypass this.