Pluginless HTML5 support for H.264 followed a similar path, in which Google promised to remove support from Chrome in favor of WebM(which FF and Opera added support for) but never did, in the meantime Firefox and Opera relied on the promise and then were forced to start implementing support once they realized Google was not going to keep the promise and it was hurting them and then included support(I don't think Opera ever did?).
Three of the four major browsers, Chrome, IE, Safari are owned by huge corporate interests and Mozilla is pretty much powerless since users blame FF if it doesn't support something, so I expect more of such things to happen in the future. It's pretty much game over at this point and I fear this is only the tip of the coming iceberg with all these companies having huge media deals for Play Store, XBox Music/Video and iTunes.