To all of those complaining that "side scrolling is a bad idea": This is a red herring. The chief complaint here is that Apple made a single gesture which in the past caused a single action (scroll to the left) and made it modal, such that it means "scroll left" UNLESS (1) the user is in Safari and (2) there is no more content to the left, in which case it means "go back".
This is an excellent complaint, and it has been raised before by users (https://discussions.apple.com/thread/3192014?start=0&tst...) and bloggers (http://www.tuaw.com/2011/08/02/baffling-inconsistencies-in-o...). It's a UI inconsistency which makes no sense, is confusing for users trying to scroll, and causes problems for developers.
Regarding reverting it, the following Stack Overflow question and answer seems to have found a solution via a github plugin:
http://stackoverflow.com/q/8737709/168775
I have no idea if it works. Good luck!