The article claims that WU's fees in El Salvador average 10% of the remittances. You can read about my experiences with bitcoin vs. WU in https://news.ycombinator.com/item?id=27448744.
> the charges are ten dollars or so, that's bearable.
Sorry, but no that's an extraordinarily privileged take. $10 is a lot of money for just transmitting some USD. And it goes a long way in El Salvador. I highly doubt the average remitter is sending more than $500/month, so it represents a 2% tax. I only consider $10 an acceptable fee if I'm sending tens of thousands of dollars.
There isn't any currency conversion because El Salvador's official currency is USD. Assuming it's WU on both ends there's no settlement risk. It sounds like pure greed.