When in the hell did Slashdot sink this low? I thought there were even moderately technically people that posted here, not people that understand computers less than my mom does.
Take a deep breath. The guy had a misconception about file types; quite unfortunately, it's one that a lot of people raised on Windows do have or have had at one point. And yes, there are going to be more and more people fitting that description showing up in forums like this one as time goes on. Unless he's trolling, there's no reason for him to willfully publicly embarrass himself. As much as his mistake offends you, berating newcomers for what they don't know yet is only going to turn people off to the field and is ultimately counter-productive. It's possible to educate without insulting, as some of your sibling posts have done. There's no reason that professional adults can't make their points both forcefully and respectfully. If educating others without demeaning them is a hassle for you, fair enough, you're not their parent and you don't owe them computer lessons. But if you don't sweat it, and let others step in and comment constructively, the field will ultimately be better off for it.