VesperArcade uploaded a series of Super Street Fighter 4 videos explaining hit boxes and frame data. Everything is explained with visual references in a clear and concise manner, so if these are concepts that you don't understand, make sure you check these out.
Imagine how many "shoryuken" or "similar move" abusers would vaporize, if it didn't hit crouching opponents. I mean, hey it was supposed to be anti-air anyway, wasn't it? ;-)
Once again, a beautiful job well done, Vesper.