The vast majority of STEM PhDs are not staying in academia. The handful of recent grads I know who did stay in academia are, as I would put it, in academia-lite. They're in industry and privately sponsored positions or institutes, that pay quite well. Take a look at, say, the Broad Institute at MIT or the Allen Institutes in Seattle. Both are large, academic institutions that pay industry competitive wages.

Oh, then if you're counting industry PhDs I'm not sure how your argument about Americans getting a premium is that well-founded. The US (like many Western countries, but to an even greater extent) has a very strong NIH syndrome, and Europeans themselves are often taught endlessly to sell themselves because they're not assertive enough in their presentations, CVs, SOPs, what have you.

And of course there's the matter that most wages in Europe in the qualified labor force are way lower in general than their American counterparts. I've always thought it was more or less due to research being underprioritized in Europe but maybe that's about to change in the light of current events ;-)