Are you saying that you are not offered the opportunity to change the selected printer at the time of printing?
I think you are referring to the printer which is part of the saved document, and not actually the "Default" printer which shows in a new document (unless you use a custom template, which could also have a printer other than your system default printer, assigned by that template.)
As with a few other apps (Microsoft Word, for example), and probably other apps that are primarily page layout apps, such as InDesign - when you create the document, the selected printer would be part of the document file.
If you open the document, you can change the printer selection (usually in Page Setup), and then re-save the document. The process might be slightly different when the Versions feature might interfere with that, but I don't have Mountain Lion to test that out on.
No, I am offered the opportunity to change the selected printer at print time; no problem with that.
The problem is indeed with the printer which is part of the saved document, and is always the printer which is the system default printer (System Preferences, Print & Fax, Default printer) at the time the document was created. That printer is then always the printer that shows with File, Print and if the system default printer has changed, may not be the printer actually wanted. I can of course select a different printer, but I have to do that every time I print that document.
You say "you can change the printer selection (usually in Page Setup), and then re-save the document", but that has no effect: the printer shown as the default remains the one which was the system default when the document was created.
I'm using OS 10.6.8 & Pages '09 4.1
Thus: the HP is my default printer, set in System Preferences. I create 100 documents: with File, Print, all the documents show the HP as the default printer.
I then change to the Canon as my default printer & set it in System Preferences. All new documents show the Canon as default, so I can use File, Print, Enter. But all the original 100 documents need the printer changed from the HP to the Canon, every time.
What I want is to change the default printer for those original documents from the HP to the Canon: I thought File, Page Setup, Format For might be the answer but it has no effect (doesn't change the default printer at that time and any change is lost when the document is closed, even if it is saved with the change).
So the default printer (the one that shows as default with File, Print) must be saved somewhere with the document file: how can I change it? There must be a way! Am I missing something simple?