Nope, didn't miss the point. The service was provided. The taxes are still payable in all likelihood (I don't know for sure). If the taxes are not payable then it should be reasonable to expect a refund of the tax component less any reasonable processing cost incurred by the airline ,don't you think?
While the customer may not be responsible for not making the flight I am pretty sure neither is the airline. Why should the airline waste time/money/valuable resources because the customer failed to show.
Buy a ticket to the movies/show/opera/cricket/football etc and not turn up. Do you get a refund? NO.
Why should airlines be any different?