Actually they're paying very competitive salaries. For example: https://jobs.bendingspoons.com/positions/67c6dc18c70c531d6db....
I can't see any salaries there but presumably they're going to be competitive for Europe, which is roughly half the competitive salary in America.
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.