That definitely didn't happen at my company. We had a round of layoffs and the package offered to people who signed an agreement not to sue only included a couple weeks of accelerated vesting. There was no performance management system in place either, so the people fired were basically just the bottom of the stack rank their managers were asked to turn in, which was often based more on personal like or dislike than performance.

There was one engineer entering his fourth year, who had saved the company 30 million dollars during his term with infrastructure efficiency improvements, who was laid off and lost millions in the RSUs that would have vested that last year (he was on a 10/20/30/40% schedule). All the ICs speculated he was fired so the company wouldn't have to pay.

Besides, if you get fired from a startup and it's not for cause, then it's probably because there are layoffs, so it might be a bad choice to exercise your options anyway.

Well, I agree with you that they should, but they don't. I got laid off from a job a few years ago when my department was made redundant, and I only had 25% of my shares vested - they let me keep the 25% that was vested, but that was it.