Windows 3.1? You'd see its full potential with Office - truetype, common dialogs and all.
COM/ActiveX? Office became entirely based on it.
Windows NT's Unicode support? Office shipped with fonts covering the whole of it.
The innovative UI elements of Windows '95 (and long file names)? Office '95 shows how to take advantage of them.
The (in)famous banner? Office got it before MS Paint.
Perhaps it's with
But now with Metro, Microsoft are telling their whole community of developers that they need to make the biggest change in the history of Windows, to completely drop their proven, decades-old development tools and habits, and embrace a radically new programming paradigm and distribution channel. This requires large investments, and investments require trust, which tends to be lost when even the leader doesn't show the way.
It's fine with any touch interface, not just a phone.
Whatever the input method, I still have to see any "legacy" desktop application getting ported to Metro while maintaining the same feature set and exposing the same functionality. Not even Microsoft themselves managed to port Office, their most important asset, to Metro, yet. Even Windows 8.1 still sends you back to the desktop for many tasks, almost two years after Microsoft officially deprecated the "desktop" development.