COL varies enormously in the US and yet even LCOL salaries are much higher than in the EU. I don't think COL is that useful when comparing salaries globally.
Also, my understanding is that in the US each person must dedicate an important amount of money to receive the health services that are provided in Europe by the administration in many countries.
not all and quality varies but generally in the tech sector I suppose they provide good quality as part of the compensation package, which also brings up the fact that generally when discussing compensation one should discuss the total package not just money (although money is generally most important)