I think you hit the nail on the head, but here's my issue: It's not so much companies like those that have a problem. I've been recruited by all the big guys on the strength of my open source work (save for Facebook, but that's probably due to a major conflict of interest, considering what I'm working on), but the real problem arises when you have smaller companies latching on to this approach, without the recruiting power of a Google or an Amazon. So now I get contacted by a small startup who all of a sudden wants me to take a quiz because they fancy themselves the next Google.