Windows have a lifetime of only 15-30 years, though. If you have to replace them anyway, you might as well get double-pane (even if the rest of the house isn't well insulated).
In my house and on my road a lot of the glass is 150+ years old.
Modern windows don't last very long, because the seals leak, and the argon gas or whatever leaks out. The glass is still good, but the insulative quality is gone.
The parent poster didn't realize that if you don't have double pane windows, you have single pane windows, which have no gas to leak.
But my point was that windows, the glass part, lasts centuries, if not longer. Not the mere decades cited upstream.