This was already-existing terminology in the IETF working-group. A "WebRTC-compatible" device is one that does not conform to the standard, but which can talk to something that does conform to the standard )in whatever limited way it supports). By definition no codec requirements can be placed on it. This was spelled out clearly in the original proposal: http://www.ietf.org/mail-archive/web/rtcweb/current/msg13432...
The IETF itself of course recognizes that the current taxonomy may not be ideal from a marketing standpoint: http://ietfmemes.tumblr.com/image/102328432749