The main Flash Player developer at Adobe illustrates a uses of H.264 in Flash player 9 in addition to On2 VP6 Codec for playing Flash Video files:

You created a pod cast for iTunes and happily distribute over this channel. Now you want to add value to it and easily make it accessible over the web without special plug-ins, reaching an audience which does not have QuickTime installed. Well, this new feature will allow you to do this. You can take your existing podcast in .m4a format and present it on any web page through the Flash Player. Add more value by adding interactivity and branding if you want to. The possibilities are endless. Link.