Performance of what? I'm not defending Flash's performance, but WebM is fine, completely acceptable. With hardware decoding continuing to advance in Flash, I guess I don't see what your complaint is. If it's native in most browsers, fallback in IE (they aren't going to care anyway) and potentially native even in IE on supported hardware...
It took them less time than it took for Mac OS X to support hardware decoding in Macbooks GPUs that already worked if you bootcamped into XP on the same machine. Though it took even longer for Flash on Mac OS X because even after Apple supported it (on limited chipsets) they didn't bother to expose it to third parties.
But now that architecture is in place it won't be difficult to extend it to other codecs. Most of the time it took to get support for hardware decoding in place was time needed for Adobe to wake up and realise there was a problem.
