> Strange that Airbnb, with their widely regarded bleeding user experience, still chose to render $ amounts without the default? "USD" qualifier.
> Was this really deliberate? Seems likely given their attention to details like this.
Random guess: maybe some US customers are confused by (or even just dislike) seeing "US$" or "USD" as opposed to just "$"? If enough US customers are like this (or even just if Airbnb believes that they are), that might influence a decision to just display "$" when they think (however wrongly) the customer is from the US.
I've never used Airbnb, so can't comment on their UX specifically, but I've seen before web sites run by US companies which offer their services to non-US customers, but have a UX which starts out by assuming you are in the US, and you sometimes have to go out of your way to tell them that you are not, and it is easy to miss doing so.