A very significant proportion of PhD students (and therefore postdocs) are non-US. Despite their meager pay (in relation to the pay that equivalently qualified

A very significant proportion of PhD students (and therefore postdocs) are non-US. Despite their meager pay (in relation to the pay that equivalently qualified people get in other sectors) the money they can afford to send money home to support their parents is not insignificant, since the purchasing power of $200-500/mo is substantially greater in China or India than in the US. This is great for them and their families, and provides cheap labor for US research establishment. The fact that they are mostly on H1B visas also prevents them from having much negotiating power with their employers, often resulting in lower-than-market pay and conditions. It also explains (I believe) at least in part why US citizens less often choose to work in biomedical research.