From: Thoughts on Flash
When websites re-encode their videos using H.264, they can offer them without using Flash at all. They play perfectly in browsers like Apple’s Safari and Google’s Chrome without any plugins whatsoever, and look great on iPhones, iPods and iPads.
I like the use of "in browsers like", since, well, those are the only browsers supporting H.264 right now (and no, the IE9 preview, right now, doesn't support any video at all).
So, it looks great in Safari and Chrome. But isn't there a browser with a bigger market share, that does support video? Oh, yeah, Firefox. So "when" you encode your video to H.264, you can be sure it doesn't work in Firefox without Flash.
Just saying, Firefox is bigger than Webkit, so if you only host H.264, you're gunna need Flash around to play those bad boys.