The ambiguity is not in the favor of anyone except lawyers. As an employee, you can:
1) Spend $100k in litigation to discover your boss owns the code
2) Get $20
Fights don't benefit anyone. Some companies would act like dicks and "ask for as much as they could get to remove it," but in most cases, that's not what happens either. A company like that would never get repeat business. Coincidentally, some employees do the same, with similar consequences. And there are employers everyone knows not to work for.
Resolving this sort of thing for a buck -- in the way a court would rule -- is really standard common-sense practice.