Update/follow up: Can this have something to do with the specific rank? I mean, does it make sense to require this for the rank of Assistant professor for some reason? Link for the posting: http://cra.org/job/umass_lowell-assistantassociate-professor-computer-science-2-positions/
I was checking some postings from cra.org, and found this remark:
For appointment at the rank of Assistant Professor, by the time of appointment, applicants must either have a PhD degree from a US university, or have at least one year as a post-doctoral researcher in a US university or US research lab.
However, I didn't find that in other postings. Is this unusual or so common that isn't usually spelled out?