This is a pretty weak point. There's hundreds of research areas and problems not worked on at the NIH that are explored in the hundreds of universities in the US. I don't see anyone switching research areas for better pay --- your skill sets are often tied to a certain class of problems. Sure, yes, there may be such effects in certain research areas. But what fraction of university budgets even go towards post-doctoral fellow stipends (when weighed against every other expenditure in a university budget)?