I don't recall the reason for this deliberate change (as seen from the docs change). 

I'm unable to come up with a good reason for this change now, but on the other hand I can't come up with a good reason for code churn and adding deprecationg warnings for a minor detail just as Raymond says.

Since the direction we're going is to allow leading zeros for all decimal literals in Python 4 (if it ever comes around), that's another reason for the status quo to win.