None of your listed reasons make a dent in explaining the massive salary differences between the US and EU.
There's a much simpler explanation: The EU simply doesn't have the capital. There are no pools of venture capitalists clustering hundreds of billions of dollars they can piss away on half-ass ideas.
It's as simple as that. They funding money simply doesn't exist.
That doesn't explain salary discrepancies between the US and the UK at the same company
A Facebook engineer in London is probably earning 70% of what a Facebook engineer in the US is earning, even after taking in to account taxes, benefits and any cost of living discrepancies.
This is driven by salary sharing companies, such that companies benchmark to each other, which tends to be lower.
For the specific case of London (and more specifically Facebook), this is driven by the fact that FB/Goog don't count tech people in finance as appropriate comparators. I suspect that this is not true in NY/USA.
There's a much simpler explanation: The EU simply doesn't have the capital. There are no pools of venture capitalists clustering hundreds of billions of dollars they can piss away on half-ass ideas.
It's as simple as that. They funding money simply doesn't exist.