This is symptomatic of the pervasive ivory tower mentality. Good UI design is about being intuitive for your users. If almost all of your users use the back button as an undo, then make the back button function as an undo, and make it do that well.

This is the same Gmail, "we'll force people to use tags even though they want folders because we think tags are better" mentality that makes non-hackers scratch their heads in wonder.