Sure, not everything is standards-compliant, nor fully interoperable. But part of the transformative effect of open Internet standards has been that anyone can implement them without permission from others (indeed, the IP policy of the W3C is pretty much engineered to make this the case).

If you want to implement a DRM binary blob with EME, you're going to have to negotiate a compliance contract of some kind with the DRM vendor, probably connected to some hook IP. (See http://en.wikipedia.org/wiki/Compliance_and_Robustness )