Holding 90% of the best engineers in the world "hostage" with six figure salaries and great perks is a good way to slow them down. I think they're scared of being blindsided, since that's what they did to Yahoo & co.
Google should be more brave and set them free. They can easily stay the best at snapping up early-stage startups. They already do this, but it should be their only strategy. Google should almost completely stop hiring direct.
I guess this is really just "Hiring is Obsolete" from a slightly different perspective. That it might be evil of Google to jealously "horde" hackers out of fear.