[freehunter]

Because cash doesn't leave a paper trail and not everyone can accept cards.

[jarek]

And third point necessary here: because U.S. banks don't have any other reasonable inter-bank transfer system.

[steve-howard]

Well, it does, but they've chosen to monetize it. I can transfer money to anyone with an account, but I have to pay $25 if I want it done today and $3 if I want it done some time next week.