Ask any geek and he'll tell you that QuickTime and RealPlayer are less than desirable to have installed on your PC, they do a few things that geeks hate.
Ask them why and they'll tell you because they both insist on running applications on start up, that means every time you start your PC, they'll have their own little programs running all the time, even when you're not using them. Even if you use the registry or msconfig to remove them, the next time you start them up you'll probably find they have changed the registry back.
Next up they're extremely aggressive and want to take over your system and all your media playback, this is a great burden for normal users who don't understand exactly what is happening, they suddenly find a new media player starting when they want to playback some music. They get a bitter taste in their mouths, often because these two players are worse than what they were using before.
They both try and sell you things too, QuickTime tries to sell you the commercial version (which you need if you want to watch video in full screen), and worse still it often comes bundled with iTunes which is even worse and in many cases can make a right mess of your existing media library. RealPlayer also tries to push things on you, their music download service called Rhapsody. This also drives users up the wall, they not only make it hard to find the applications on their own by bundling other applications you don't want with them or by tricking you into downloading a trial version rather than the basic free version.
I often have to sort out people's computers after they've got half a dozen media players installed usually which they don't need, yet often all of which are fighting each other for control of the system, constantly asking if they want to be the default player and taking over file associations. This sort of nonsense has to come to an end. Apple and Real have to learn that users need to feel in control of their computers or they'll just avoid using them.
So what do I recommend instead? Well if you really need support for QuickTime and RealMedia use QuickTime Alternative and Real Alternative instead. Both allow playback of QuickTime and RealMedia in a simple and under control fashion, without all the extra bloat you don't want.