Not all choice is bad, but not all choice is good either. The choice between using windows or linux is to a degree a different kind of choice than the choice of, say, between xfce4 and gnome. (Hint: in the latter choice, you can still run the same application binaries.) Since applications are the thing that truly matter, window manager choice looks trivial to me. And window management? *sigh* Really, are we talking about things like closing, moving, resizing, minimizing and maximizing? This stuff was boring in 1995.
It's also a valid point that a different hardware setup requires a different paradigm. Whether Weston can adapt to, say, mouseless and keyboardless window management is a separate question in itself, but at least different interface devices undeniably pose different requirements.