(Erg, first post eaten by mis-click.)
Three points why I think that this is not the real reason for the problem.
1) Personal experience. I am an immigrant to the US. I probably cost my employer *more* than my peers due to legal fees, admin work, etc... before I got married. Throughout my tenure, my salary has always been comparable to peers. Sometimes it's a little lower (because I just started working in an area), sometimes a bit higher (once I have become tenured in that area), but on average identical. Between all of the additional costs I incurred annually, I was certainly less cost-competitive than others and that will be true of most people here on visas (except at companies likely to encounter some future legal difficulties).
2) Companies *everywhere* complain about this. Our clients in *India*(!!) complain about this exact problem. Not only that, but it's companies in all industries, for all types of jobs. This is far, far from being a tech-specific problem and therefore far, far from being a specific-visa problem.
3) Later in the article, there is a very good section on the shortage of good, experienced HR managers and how this has allowed hiring managers to expect to find employees that can plug right in without training. As much as we malign HR, too many good HR people were laid off in the recession and it's had an impact on managers' expectations when they post jobs and consider fit for role and the need for employee onboarding. I suspect that this shifting expectation about training is the real root cause.