Problems with interoperability are temporal for WebRTC for Firefox and Chrome.
It simply take time to write software properly.
While MS demo prove nothing as SAME development team create both parts. So Google implementation could still had same problems with communication with MS…
But at least its fight within IETF and W3C. That is good and it may result in superior standard (as happened with touch standard proposed by MS), even if MS use it as usual for some purely PR’ed claims.