How did the function "Save As…" change to "Duplicate"? I recently noticed that within Pages ('09), Numbers ('09), Keynote ('09),
the menu entry:


File > Save As…


had been replaced by a new one:


File > Duplicate


On the other hand I still use this function within some other applications like LibreOffice (4.2.3.3) without a problem.
I suspect this change isn't a system wide one.

I didn't get any notice of this change of a key function in file management within any recent upgrade.

When did this change appear?

Which upgrade performed this change?
This was changed in Lion along with the introduction of Auto Save and Versions. Save As is still available by holding ⌥ alt whilst in the menus.