I've not run into any RPGer who takes this attitude in real life but quite a few of them on the internets. Crazy internets people. There is something to be said for knowing what you like, but being derisive towards others over them not liking what you like is silly. And you should stop it if you're doing it. I recommend trying a new system every once in a while. That way you can find out if D&D is really the only system you like playing. If it is, good for you. If not, you're missing out.