There does not seem to be a way to expand the text-area size or goto the bottom of question/editing boxes. It I were to edit a long post I cannot find a way to get to the bottom of it. The only text I see is that which is already visible without scrolling.
Can't you scroll with two fingers? I don't have an iPad but that usually works.
Indeed, here is a video Ben made of him scrolling the text area using two finger scroll on the iPad 2.