> doesnt mean the inside one isnt there to protect the outside one.

The inner pane is typically half the thickness of the outer pane.

So whilst you could argue it cold be seen as a failsafe, I would say its primary purpose remains "double glazing" insulation.

The OAT at 30–40,000ft is very low and there is a lot of combined window area. So the importance of insulation is not to be underestimated. In particular on newer aircraft where efficiency is the name of the game in their design.