Apple reverses scrolling by default. I don't know about other coders' computers, but there are people who don't know how to change it, and whenever I boot into recovery mode it gets reversed.
It's only "reversed" if you consider the other direction "normal". Either one makes sense: Mac acts like your finger is moving the page itself; X11 and Windows act like your finger is moving the location indicator on the scrollbar. Either one makes sense a priori, but once you're used to one the other becomes intolerable.
