Yes outsourcing to the UK where the average salary is ~$37,000 is I'm sure highly cost effective for US firms. Where we'd reach to say India for cheap labour the US now comes to us. I've seen US Interns get paid more than the vast majority of brits. Even the average dev salary is only say, double that average. Not even accounting for taxes - which supposedly cover healthcare but almost none you can readily access.
Dev salary being double the average national salary is very good by western EU salaries. In Austria for example as a dev you earn just slightly above the national average income.
I think only in the US and cheap countries like Poland, Romania, SE-Asia, etc it's normal for devs to earn several times the average national income because they're hot markets for tech outsourcing and average national wages are on the low side for those not working in tech making the gap really big, but in western Europe dev wages tend to be around national wages out side of big-tech.