"Google in a defense of its decision to pull H.264 from Chrome's HTML5 revealed that it will put out WebM plugins for Internet Explorer 9 and Safari. Expecting no official support from Apple or Microsoft, Google plans to develop extensions that would load its self-owned video codec. No timetable was given."
So Google gets started with their plan for world-wide WebM domination. They'll provide WebM plugins for the browsers of the H.264-only league, so in practice, all mayor browsers will have WebM support –one way or the other.