[gumby]

The existence of such programs merely says there are enough users willing to install such programs that it's worth making them available (and that macs have the affordances -- APIs -- to make these kinds of changes, which ios does not have). There are so many macs in use that a tiny percentage is enough.

I suspect the same is true in the general case in the ios app store: that there is a long tail of apps used by a tiny %age of users, but with an enormous user base that's enough to make a free or even paid app.

And after about 35 years of mousing and about four years of iphoning I expected to want to revert apple's change to mouse-gesture-scrolling with Lion, but after only a few seconds I was sold. YMMV, of course, but I agree with the "99%" hypothesis.