Hi timethief - I didn't misunderstand you - I don't think.
I found the Visual Editor. Yes, logically to enable the Visual Editor, you would want to leave disabling it unchecked which is the default. Leaving it unchecked does get me a post window with two tabs. It always comes up with html tab live and a Visual tab in the background next to it. When I click the Visual tab to switch to that, it highlights but does not change away from the html tab.
BTW, I have a second WP.com blog. I checked there and to post on that one, it comes up in the Visual tab with all those toots and whistles and the html tab showing in the background to use if desired.
So, go figure. I have a feeling the software is corrupted in the blog in question.
I sure hope someone knows the magic needed to fix this.