1. It means they're scared. Companies wouldn't do this if they were afraid of a 10% bump in salaries. They'd just pay it out. That's small compared to the cost incurred by constant churn, code turning into legacy as people leave the company, etc. To pull that shit, they're worried about something larger.
2. If they were able to pull that "cartel" off (and such arrangements are inherently unstable, because it's always in the individual interest to break) it would be stupid for them and advantageous for startups. If the big companies hold each other back ("crab mentality") then startups would have less competition for talent.
In fact, the second contradicts the intentional over-hiring observed at large companies: why do these huge companies pay $150-250k for people to do mind-numbing, unnecessary maintenance work on zombie projects? (I've seen legacy monsters at large companies with 4 full-time maintainers.) Because they don't want these people in startups that might threaten them, 5 to 10 years down the road. Fighting to keep down salaries just seems to increase the likelihood of this happening.
Except when the best of the best want to go from Apple to Google, specifically. And can't. It's not just about salaries, it's about prohibiting professional growth. And I would be very surprised if it didn't keep salaries down.
