Apple's OS X Lion introduced Auto Save, and eliminated the Save As feature from several apps as a result. Not everyone is happy about the switch, including Pierre at Betalogue:
I have already talked about the totally unnecessary (in my view) elimination of the 'Save As...' command in Apple applications, including the iWork suite. The 'Duplicate' command that replaces it is simply not a good enough replacement, and the change irremediably breaks well-established workflows that cannot be adapted to the new command."
Amen, Pierre. He goes on to illustrate the various stumbling blocks that Auto Save and its Duplicate feature introduced. It's worth a read.