There's no controversial changes in python3? Except if you consider print() controversial but that's so silly it's laughable.
There are however non backwards compatible changes, like unicode by default, IE7 was also non backwards compatible so the comparision still holds. (with the exception that IE had a compatibility mode if you sent some magic http headers)
It can be silly, but that was one of the reason I picked Ruby over Python 5 years ago for a project. I felt at the time, Python is awesome, however they are taking a weird path.
There are however non backwards compatible changes, like unicode by default, IE7 was also non backwards compatible so the comparision still holds. (with the exception that IE had a compatibility mode if you sent some magic http headers)