This is the change that breaks most existing Python code.
Why change from a statement to a built-in function (BIF)? Having print as a statement is limiting in many regards, as detailed in van Rossum's "Python Regrets," which points out what he feels are shortcomings of the language. Having print as a statement also limits improvements to it. With a function, new keyword parameters can be added; certain standard behaviors can be overridden with keyword parameters; and it can be replaced if desired, just like any other BIF. Consider these before-and-after examples:
>>> i = 1 >>> print 'Python' 'is', 'number', i Pythonis number 1
>>> i = 1 >>> print('Python' 'is', 'number', i) Pythonis number 1