even for people in the US, it was not really easy when Mtcocks stopped taking their money
And why should an exchange open up in Argentinia, to accept large amount of weak local currency, for BTC? What would they do with that local currency? They cannot move it out or convert.
In Cyprus the story was different, the currency was Euros. Only the bank transfers to the outside were halted.
It should be relatively risk free for an exchange, as they hold both the bitcoins and the fiat until a trade is done by the users. The risk is on the bitcoin seller, but that should only skew the price, trades should always be possible. It's just like the blue dollars.