That is one of two ways to look at it. Most employers do not think of the initial stock as a grant that you have earned for signing on and then four years of dragging out payment. They look at the stock as four years of payment that, along with your salary, is designed to keep you motivated the entire time. So, the other is:
zynga: want to be an early employee in our risky little venture?
emp: um - the salary is kind of low and there's no job security
zynga: we'll toss in 25,000 options per year for the first four riskiest years. potentially worth $2.5M per year if our stock hits $100 in the ipo
emp: okay, that sounds better. i'm in
2 years later
zynga: hey, looks like you did pretty good the last two years, but the trajectory of the company has changed, there is no longer any risk in it for you, and it doesn't make fiscal sense for us to pay you $2.5M a year in stock anymore. We'd like you to stay on, though, and you'll still get a competitive salary and benefits plan. If you don't think that it is competitive, we understand.
The problem is structural. The spirit of a 4-year vest is that you should keep the employee (if they are good) and let them vest at the original rate. But if the company suddenly becomes massively more valuable and less risky, the incentive is to fire that employee and hire someone else, because you can.
I think it is incumbent on us, the startup world, to call this out as bad faith, which is what it is. Legal or not, companies that do this should be forced to walk down the hall of shame. Their founders, if they are around and party to it, should be unwelcome in our midst after reneging on the social contract that makes this whole thing workable.
They are shitting on the commons, and spoiling the fields for all of us, by making the decision to work for a startup that much riskier.
What you're saying would be true except that if the employee saw that the company was headed nowhere and they left after 2 years, nobody would say, "Hey! But you agreed to a 4 year plan. We have paid you all of this stock that you haven't vested yet."
zynga: want to be an early employee in our risky little venture?
emp: um - the salary is kind of low and there's no job security
zynga: we'll toss in 25,000 options per year for the first four riskiest years. potentially worth $2.5M per year if our stock hits $100 in the ipo
emp: okay, that sounds better. i'm in
2 years later
zynga: hey, looks like you did pretty good the last two years, but the trajectory of the company has changed, there is no longer any risk in it for you, and it doesn't make fiscal sense for us to pay you $2.5M a year in stock anymore. We'd like you to stay on, though, and you'll still get a competitive salary and benefits plan. If you don't think that it is competitive, we understand.
emp: works for me. (OR) doesn't work for me.