Unless you are getting pretty fancy in Word, why not use a full featured WordPress editor (I use WP Edit Pro) and just paste it in as text and then do the formatting in the WP Editor.

I'd imagine that from the tinyMce (the editor WP uses) end of things they've decided that there are lots of various word processing programs and they all use their own flavor of coding to format things on a *paper* page - far too many programs to keep track of.

Also, even when the "Word" button did exist, it was no panacea. It left lots of crappy and unnecessary code behind. I even had a few clients who used the Word button to paste in from Word and it looked fine... In every browser except Internet Explorer!!! In IE no text on the page was displayed at all!!!
What??? A Microsoft program that couldn't read Microsoft coding? What a concept!!