Actually they're paying very competitive salaries. For example: https://jobs.bendingspoons.com/positions/67c6dc18c70c531d6db....
There are plenty of competent devs outside America. I can't see any reason why you'd want to pay American salaries if you're a global company.
> Typically, we offer individuals at the start of their career an annual salary of £85,797 in London and €66,065 elsewhere in Europe.