"Zynga's argument is that they don't want people who joined the company early to get disproportionately large rewards compared to someone who joined the company

"Zynga's argument is that they don't want people who joined the company early to get disproportionately large rewards compared to someone who joined the company later but contributed more." And we can stop right here. That's an excuse, not a reason. It's purely PR bullshit to make it seem like they're trying to do something right. It's nothing more than the company (whether executives or investors) going back on their word when they realized how much money their stock was going to be worth at IPO. This is one of the biggest reasons I loathe Zynga.