These are two great articles by James Hague on text processing vs visual programming.
His main point is visual programming is often dismissed because it is way more difficult than text processing. It is a little bit like a lot of "stupid" things in the world such as Windows programming. They are actually quite tough to do well.
On speech processing, I guess it is appropriate to think sound programming is tougher than text processing as well. You may even think in speech processing, no one come up with a generic "Sound User Interface" IDE yet.