Never heard of XE.com before this, and not sure why anyone would have...
Absolutely no reason why anyone would, unless they work in financial services or related. Not sure why PK would make the claim that 'you've probably used it' based on this audience.
Totally not true! I used to use XE.com all the time when I used to import games...
I would have never thought that the co-founder of a currency site that I've been using for 3 years while living abroad for school is a BIG fan of Double Fine and video games in general. It is just fucking amazing. I would have imagined that the co-founder of a currency site would have been some stereotypical business magnate.