How do they deal with the superior energy efficiency of new windows? Even basic vinyl windows are better in terms of energy transfer, unless they're replacing the window frame with more modern equipment (factory made vinyl/aluminum) while keeping the original windows.
You could replace the glass with it yourself if you order the correct sizes.
That's even better as a product than triple-glazed windows.
Argon sealed double panes aren't magical in terms of R-values.
For the glass itself, you update it to something better than a single pane. Or put a storm window as needed.
Although energy efficiency in these homes have other problems. The walls are probably not insulated (and probably shouldn't be without a vapor barrier added outside beneath the siding - otherwise you will get lots of mold over time) and the weight box for the sash's are not insulated and can't be unless you want the window to no longer function, which may be OK as you can seal around it then.
The actual issues, in order of importance, are:
1. Air sealing the house. So yes, replacing and repairing windows. Not because double pane is so much better, but because your windows and doors are leaking unconditioned air into the house.
2. Roof insulation
3. Basement/crawl space insulation. Yes, this is more important than walls
4. Now you think about the walls. As you said, depending on the climate, from outside in may be safer (which can also be true for roof and basement depending on materials)