To me the larger question is whether or not GPLv2 achieves the goal of forcing big companies to contribute back to a project better than a more permissable license does.

As stated in the article, Linux is the notable success story, but anecdotally it seems that the majority of projects with large company contributions are licensed with BSD/Apache/MIT but with contributor agreement attached.

I wonder if anyone has compiled any data on whether GPLv2 does actually encourage contributions more than the more permissive alternatives.

GPLv3 isn't even worth mentioning in this context, great concept, abject failure to thrive IMO.