"Duplicate" is a better way of doing "Save As…" anyway.

Duplicate is better than the old system, as you say. And so is Revert To Saved, which works way better than the old Quit and then answer "No" to "Do you want so save your changes?".

You get the same functionality with basically the same number of keystrokes overall, but you get a LOT more flexibility and a lot more safety net under you with the new system.

For example, if you make some changes, then decide you don't want them and you Revert To Saved, then Quit, the document will look just like it was before your changes. Drag-n-drop it, attach it to an email, it is unchanged. BUT you can actually retrieve the changes in the revision history if you later decide you want to look at them, or copy some of them, or actually use that version. A LOT more flexible, unless you're worried about subpoena's and want no evidence you ever thought of making any changes. (In which case, you should be worried about temp files and all kinds of other issues.)

It's just old habits that die hard, really.

I personally the old Save As…

But that's just me.