The special consideration is in the stock options and MAYBE the subsequent position they are offered and not necessarily in the relative compensation for that position.

They usually DON'T stay. But when they do, it's usually due to stock option vesting plans.

The importance of "stay" is in the context of the acquiring company, not the acquired one.

If an acquiring company treats founding employees the same way it treats the other acquired employees, the founders are likely to run for the door the moment they legally can. Maybe that's OK as far as the acquiring company is concerned. Maybe not.