Having spent the bulk of my career working and living in the Silicon Valley, this type of anti-poaching tactic was tried back in the the 1980's as well.
It was quite common for a sought-after Valley employees to jump companies every 2 years or so, and with it, get a bump in salary of 15-25% or more. Companies tired to stop this job hopping back then but to no avail. And I say 'why the hell not let my services go to the highest bider"? I personally have no issue with it. If one believes in capitalism and free trade, and the Valley is ground zero for people with those beliefs, then this is just an extension of that. Last I checked, the Execs of the companies in question practice that philosophy, right? And the Execs of those same companies get golden parachutes, massive bonus packages and other perks, as well, so, as they say, whats good for the goose....