The lower salaries are probably due to the lack of VC funding, which in turn is rooted in a lack of really successful European tech companies.
If you work for a European company, chances are it won't grow and be successful to the same extent as an American one, and therefore your work has less value.
Nope, that's just in the USA, us in Europe not at all.
And I'm not even comparing EU salaries vs US salaries just tech salaries/property prices ratios for each location.
You're not overpaid, it's us that are severely underpaid in comparison.