Why shouldn't companies retain employees by paying them what they are worth and giving them a good work environment rather than colluding to keep them from leaving?
It's not about colluding, it's just that the new CEO is bound to not hire you out of loyalty to his/her friend. Social laws and laws on the books don't always line up well.
Almost nothing in business is purely professional, that's like ignoring friction in physics problems. And when it approaches that state, the results can be pretty amoral and scary. Part of being a good CEO is being a good human. Companies aren't perfect abstractions from the underlying humanity, nor should they be.
col·lude (kə-lo̅o̅d′)
intr.v. col·lud·ed, col·lud·ing, col·ludes
To act together secretly to achieve a fraudulent, illegal, or deceitful purpose; conspire.
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Seems like colluding to me. Just like in the Google/Apple/Adobe case. It doesn't matter if it's done out of friendship or fear of upsetting almighty Steve Jobs.
If his CEO friend didn't know he was doing this, they would not be acting together - the friend would not be performing any action at all. But if they communicated with each other and agreed to act this way (like Apple and Google did), then it would be collusion.
But even if it wasn't outright collusion, it could still be ethically questionable to limit another person's opportunities just because you're afraid of losing someone's friendship.