In university I used Word 2007 to type math lectures in real-time. I never had to resort to the mouse at all for equations. You seem to be thinking of the stripped-down MathType equation editor that was bundled with Office for a while (before it had native math support). The PDF you linked is for Office 2007 onwards and shows that the markup language you mention is mostly like TeX with a few simplifications, e.g. smart handling of things like x^12 which is then actually x¹² instead of x¹2. Basically it uses parentheses where TeX uses braces and needs a lot fewer of them because of more natural tokenizing.
I think you're right. I plan on trying it, next time I need to enter equations into Word. For me, the key to ergonomic use of the computer is being able to look away from the screen. For instance, I can type text forever without constant focused eye contact with the screen, which greatly reduces the eyestrain issue.
And I suppose a useful thing is that if you do misspell one of the keywords, it just sits there until you correct it, as a reminder of what you were trying to write.
