Of course this is just anecdotal, but I haven't had a LinkedIn account in 5 years and have had many job offers. I have never heard of this being a prerequisite or even a contributing factor.
It's not about immigration. HR people are talking things like that on seminars for people looking job in Poland :) And they're using such argument so people would create accounts there. So, by reading your comments it's more BS of hr people for theire on benefit.
> Sending resumes will get you jobs, knowing people is not the only way.
Right now, yes. That was true in 1998, too. In 2001, if you didn't know someone you were welcome to wait in the unemployment line with everyone else. You don't need an account on some data-grubber, but I would suggest very strongly that you invest in some kind of professional network. That doesn't mean a web site, it means a group of people you've worked with who can vouch for your skills and would like to work with you again. There will come a time that you will be nowhere without it.