Re: How it works:-
forcing staff to not sell for 3 years also stablises the share price, an effective anti-short off your own stocks.
HMRC regulate the scheme and insist that staff not be able to sell until the end of the lock-in, and further that they forfeit any shares not held for 3 years at the time of resignation.
Most FTSE 100 companies have a similar scheme, so its not really an Amazon issue. All listed companies have the same opportunity; I'm not sure about unlisted companies, but I don't see why they couldn't set up a similar scheme.