I'm going to take a slightly controversial position here - so please read through my logic before you downvote me into oblivion. If you read the article, you'll see that what's happening at Zynga is not "Taking Back" stock, instead it's talking about _future_ compensation. Every time I've been through a Compensation Review - one item that is made very clear to my manager, is how much _unvested_ stock I have in the co…
The typical option agreement says that the stock you may purchase is subject to a right of repurchase by the company, and that right (by the company) lapses over time. So, I imagine that is totally negotiable until such time that that right lapses. It means going back on your word from the time of hire, but corporations go back on their word all the time, usually because it's believed to increase value for shareholde…
From that perspective, there isn't much difference between (A) Vesting Stock, and (B) Lapsing over time a Restricted Repurchase agreements.
Nobody is going back on their word - it's just a different way of vesting.