If you are in international airspace, you are obviously on an international flight - and scheduled carriers usually don't charge at all. I guess you could be talking about charter outfits ?
If charter, the share thay get of your holiday package must be pretty small after the hotel is taken out of what you paid, so I am guessing that the exorbitant drinks prices help them to stay in profit
As regards "long-haul international" flights on scheduled airlines, I'd personally prefer to pay a reasonable (duty free!) charge for a drink, as I sometimes feel a bit of a freeloader when asking for a second or third soon after take-off when I've already done one long sector and want to sleep for the next 7 hours
Haven't had a drink on a domestic in Europe for a while, but a couple of dollars seems to be the going rate on US domestic sectors - not too bad!
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What goes around . . .
. . often lands better!