Oh, don't get me wrong. I definitely prefer a more style-sheet oriented way of declaring how a document should look, and then writing my document tagged in the elements of that style. Something style-sheet oriented is vastly superior to something more formatting-oriented at a lower level.
The problem is that most GUIs, in an effort to reduce clutter, make it at best cumbersome and at worst impossible to determine if your cursor is inside or outside of a formatting tag. (And then there's Word and Outlook, who add a bunch of heuristic behaviors on top of that that just make it worse. I've had to nuke whole paragraphs just because there's some weird 'hot point' in the middle of a line somewhere that keeps making the editor go gonzo. FrameMaker is not as bad, but it gets weird in other ways, especially with figures, tables, their anchors and their captions. And then there's the brokenness of nearly every browser-based rich-text editing widget ever.)
I would much rather have a WYSIWYG preview and a separate, less WYSIWYG editing mode that was more tag oriented. Heck, I'd write my specifications in TeX or LaTeX if they let me. But, alas, I'm stuck with FrameMaker and Word. At least with FM, they force us to never use local formatting overrides and stick to the style sheet. They strip all formatting overrides when compiling a book.