When you click the Reply Options button, you get a much better reply space. It contains several Rich Text buttons and importantly you can change pages in the topic you're replying in without losing what you were writing.
The basic reply box at the end of a page or topic not only lacks these buttons but doesn't retain an in-progress post when you change pages. I have nuked several paragraphs of post several times by now and every time it is infuriating. If the crappy text box was removed so the good reply box was the only option, it would be consistent and remove this constant risk.