RealPlayer was a program and browser plugin focused around one proprietary format. QuickTime is an A/V library supporting a wide array of codecs — it's the standard way to play video on the Mac. If it's obsolete, then what is the replacement?
That isn't an alternative; it's an orthogonal technology. Saying the video tag renders QuickTime obsolete is like saying the img tag renders libpng and libjpeg obsolete. HTML5 video is a standard for specifying video files to play — it doesn't actually provide video playback. QuickTime and its codecs are still used to actually decode and play the videos (again, I'm talking about the Mac here).
You are not making any sense. You say that Quicktime is outdated technology and has to be banished, yet you are okay with browsers using it to display HTML5 video?
How does that work? On Mac OS X to do anything with video you use QuickTime. QuickTime isn't just the front end software. It provides an API that can be used to create all kinds of software, not only that it allows other codecs to easily be installed (see Perian for Mac OS X).
