Why is it that Firefox has a debugging add-on that supports Drupal development but we yet have to see a Drupal add-on that supports writing for a Drupal site? It's in times like this I so wish I were a coder.
The problem arises with the myriad of input formats Drupal has just by default (forum, blog, story) that gets complicated when you then throw in the forms for Event and or Calendar, Image, Audio, Video, Storylink, Quotes, Recipes, and all the customized formats possible with the Content Construction Kit (aka, CCK).
And then there's the little detail of taxonomies.
ScribeFire works amazingly well just for the blog, page, story, formats AND only if you have a relatively small amount of categories (in the low hundreds). If you have more than 300 categories, the add-on is incapable of reading them all. Not only that, when it does read the categories it outputs them as selections --it really doesn't allow you to search through all your categories and choose only the ones you need. It neither allows you to add new ones on the fly.
This is the problem that arises from trying to make a tool that is something for everybody. It works well with WordPress and Blogger and Movabletype/Typepad blogs because they all have very similar information architectures. Drupal is a beast on its own and that's why it needs its own set of "off-site" blogging tools.