I'm in the highly skilled category myself, and half the people I interact with have been there at one point or another. From what I have seen, the kind of person who is willing to relocate to a new country for a job opportunity is likely to do so again, should a better opportunity arise. Many people I know have worked for a few years in the US, but most of them have left for better opportunities elsewhere. And once they grow older, the "better opportunities" are more likely to involve living closer to friends and family or a good environment for raising kids than higher salaries.
The immigrant/emigrant question is a matter of perspective. An immigrant to one country is an emigrant from another.
H-1B is a dual-purpose non-immigrant visa. When you have obtained/extended your H-1B status and are applying for the entry visa required for international travel, you are required to provide a permanent address outside the US. Once you enter the country, the immigration officials really don't like it if you claim you are living in the US. And because H-1B workers are not US residents from immigration perspective, most of them are currently banned from entering the country if they have visited places like the UK, Schengen area, or India in the past two weeks.