Discovery is a thing. Big companies are more likely to catch these shenanigans, making it automatically a legit term, and also more likely to have retention policies where you can get it later in discovery.
It's not a big corp vs small corp distinction; it's a question of how important the employees in question at the company are who were in the more powerful position. A large company isn't going to bend over backwards for a seven rungs down middle manager committing the wrongful termination, but when the most influential members of the company are involved all the stops come out. It's just more likely that a small company involves extremely influential to the company employees.
You're right about smaller corps.