I'm a dev manager at a prominent employer of software engineers and I did a search for my company at your link. I can't speak for other employers, but it appears that salaries for H1-Bs are ~25% lower than what I know Americans to be making at those same job titles. Half is almost certainly an exaggeration, but to deny that there's an H1-B discount is equally disingenuous.
On the topic of the essay, I worry that Paul is also being disingenuous. The US might only have 5% of the world's population, but we have a much larger percentage of the world's population where children have been exposed to computers from an early age. He's right that exceptional programmers can't really be trained, but that doesn't mean that they aren't made. They're made by being put in an environment where they can explore computing and let a natural creativity/curiosity that they have flourish. I've yet to meet an exceptional programmer that begrudgingly chose to write code for a living.
And that's my problem with the H1-B situation and why I think they've got an overall lower percentage of exceptional programmers. In the US, those who are driven by extrinsic motivators like money don't become programmers. They become salesmen, stockbrokers, lawyers or any of a host of other professions that sacrifice doing something interesting for high compensation. But most of those career paths aren't available to people in poorer countries whereas software engineering is. What I've seen among H1-Bs is a far higher percentage of people who basically hate their job, but do it because it allowed them to come to the US and afford a comfortable lifestyle for their families. I don't blame them for that, but I also don't think that it makes them particularly good developers. Don't get me wrong...I have met quite a few H1-Bs who were drawn to software development from an early age and love doing it in the way that usually results in being an nx developer (anywhere from 1x to 10x), but I just don't see them in the same proportions that I do among American developers.
If Paul can figure out a way to filter in the great developers while filtering out those that are only coming to make money, then I'd be completely behind his plan to let them all in. Somewhat ironically, his plan to let everyone in would somewhat accomplish that at the cost of decimating developer salaries (i.e. if the labor pool is increased and salaries dip accordingly, we'll find out pretty quickly who's only here for the money and which of us would be doing this no matter whether we were paid significantly less.)