You are wrong, please test it again. In Word 2010 it still uses the Frontpage engine to output not so good HTML4 code with VML graphics. Btw. Office applications haven't changed that much since Office 97 (beside regular interface changes).
And just because some have never have seen a good HTML WYSIWYG editor doesn't mean it's a bad rapid development method and should not be integrated in a modern IDE.
- contains VML code
- will not render correctly in any modern browser
- If you want to be able to render it in IE11, you have to press F12 (Developer tools)
and change from "Edge" to compatibility to version 7 (or even 5) of the IE engine.
Then it will be drawn "correctly".
To clarify the generated code is invalid HTML 4.01 (20 errors according to W3C HTML4 validator https://validator.w3.org/check ) and the first view lines look like this:
Microsoft split Frontpage in two products SharePoint Designer and Expression Web (the later with a new web render engine), though both products are either a shadow of the former self (no WYSIWYG view anymore) or abandoned (free download without support): https://en.wikipedia.org/wiki/Microsoft_Expression_Web
Wordpress uses the TinyMCE rich text editor which uses the contentEditable/designMode API, TinyMCE is one of many such editors that try to fix many of the glitches: https://en.support.wordpress.com/editors/ , http://www.tinymce.com/ , https://en.wikipedia.org/wiki/Online_rich-text_editor
And just because some have never have seen a good HTML WYSIWYG editor doesn't mean it's a bad rapid development method and should not be integrated in a modern IDE.