As said above, most countries do it, they tend to be more subtle than the tax introduced in Argentina, and force it into the ticket, so you blame the airline. Ireland have introduced another exit tax this year, much to the chagrin of the travel industry, especially during a recession when tourism is falling anyway, but what do they care!
Again, as said above, when I last left BsAs last month, the exit tax was included in my ticket and the check in desk just stamped my ticket saying it was paid. When I left in March, I assumed it was, as that has become the norm around the world, and had an argument (to no avail) with the security folk, naturally I lost and had to go and pay at the booth.
I remember flying out of Bangkok around 20 years ago and having no money left, and ended up "borrowing" a few bhat from a fellow traveller so I could get on the plane. The locals were unimpressed with my arguments I had no cash (and no credit cards in those days), I would bet a few backpapckers have been through similar....