In the Netherlands the average salary for a senior developer is 40.000$ (~24.000 after taxes) while the cost of living is not that much different from the UK and US, may be except for healthcare. What exactly justifies the difference?
In the end, it all comes down to: why are these people, who could do it, not moving from the Netherlands to the UK or US?
They are probably 'comfortable' in the Netherlands, whatever that means.