High school graduates are expected to know about 2000 kanji, BTW.
Yeah, that's what I was taught in my Japanese classes, but it's not true. Come here, and you'll see that katakana is used for many things.
furigana (pronunciation characters) over people's names,
sound effects in comics and on TV,
foreign words of course,
even regular words (if you watch enough TV, you'll notice that).
As for that last item, I have repeatedly asked my (Japanese) wife about why they use katakana so often on TV for regular Japanese words. The answer? I don't know.