[kaizendad]

I am absolutely not clear how changing one's IP is different from any other form of currency arbitrage - which is what this transaction is, and also what explains the cost difference between currencies from the airline's point of view - their native currency is easiest for them to transact in, and they pay additional costs to transact in other currencies.

In fact, the airline probably appreciates being paid in its native currency. Airlines from countries with currencies that aren't always easily convertible, such as airlines from the developing world, probably have to keep substantial reserves in currencies their customers tend to use, to ensure that they can always carry out transactions in that currency. If you buy your ticket in the native currency, then you've not required them to dig into that reserve, which is a win for them.

Conversely, this is probably not a win for the original questioner, because they probably paid a fee for currency conversion to their bank, which was probably larger than that paid by the airline, because the airline has more market leverage with which to set pricing contracts for currency conversion.