I want money from XE.com for endorsing them in this thread! I'm gonna email them right now and demand some kind of tshirt or something. 😛
Anyway, yeah, XE makes their money (on "free" transaction) by charging slightly more to buy money than they bought it for. If the going rate is 6 GACH per 10 DOODOOs, and PayPal will let you trade in 8 GACH to get 10 DOODOOs, maybe XE would charge you 7. Money transferring is all they do, unlike banks who have overhead and all kinds of stuff. So XE still makes a little bit of "profit" off the transaction (in this case 1 GACH over the going rate). That covers all their fees and provides them some income. If you're transferring a fairly good amount of money (a few thousand dollars at a time) then you're usually going to save 5, 10, maybe 20 bucks over what you'd get from PayPal. That adds up.
Also the actual transfer process is kinda cool. Once you log on, and tell them how much you want to exchange and what accounts to do it to and from, you go to a page that shows you the rate up to the current minute. You can watch it and keep refreshing, and actually see it fluctuate. When you're ready, you click TRANSFER and your rate is locked in. I think it's mostly just a gimmick, but it always makes me feel good to get what I think is the best rate at the time. It only moves by a couple dollars or two overall in the short term, I guess.