Well, I'll admit, that is one risk that Japanese salarymen don't have to deal with. That said, are you sure that is realistic, and not just engineer-is-totally-terrified-of-confrontation talking? It is a seller's market for engineers, even at big megacorps. A manager would have to be insane to threaten firing over "We're going to miss that deadline if you add this", especially because firing guarantees that the deadline gets blown and everyone in the room knows it.
It doesn't have to be an outright firing (GP never used the word 'fire'), it could be that you'll get passed over for promotion or just given maintenance work until you leave.
Being taken off a project and being replaced with someone else isn't going to look too good either way, especially not if the someone else manages to do what you said couldn't be done (you're obviously sure enough of yourself that that would never be the case).
That said, are you sure that is realistic, and not just engineer-is-totally-terrified-of-confrontation talking?
I'd say it is more realistic in other places than it is in Japan and similar social cultures.
The limiting component is one's sense of honor and loyalty to one's company. In a culture where honor iand loyalty sn't so prized, a manager would have no problem firing an employee in an attempt to deceive people.
Sure, it might blow the deadline, and everyone will know that, but it will shelter the manager from responsibility. If the manager can intimidate the engineer into accepting the new feature on the old deadline, then the manager can claim it is the engineers fault for blowing the deadline. If the manager can't intimidate the engineer, and instead fires him, he can claim he would have hit the deadline if he didn't have such an incompetent staff underneath him. Either way, it's not his fault. Sure, it might screw the company, and it will definitely screw the engineer, but at least the manager is safe.
And yes, there are a lot of organizations like this where responsibility does not follow authority. But it requires a complete disregard for one's sense of honor.
From the conversations I've had with my dad regarding Japanese culture -- he was stationed there while serving in the military --, I get the impression this sort of dishonorable behavior is almost inconceivable over there. That might be why it seems so unrealistic to you. :-\
