I don't know.  That has to be applied very carefully to work effectively.  There are more places it doesn't work right that where it does, and it's really annoying to have things scrolling when you don't want them to.  With full-screen, single-screen Metro apps, it works better than something like a desktop app.  But even there, you have corner hotspots, and potential second monitor, simply bumping into the mouse, etc. that still create things to "reach for" and could trigger scrolling when you don't want it.  Within small controls it would be much easier to implement the scrolling without unwanted side effects.  It should be OS-supported behavior that is available, but default may not be the best thing.