Compare to other companies that have done the same, like AT&T wireless (hello iPhone users) and to places like BoA that are up front about training replacements but will [threaten to] withhold all severance pay should the employee refuse.

And the severance the Hyatt folks were give (if the below is correct) is about twice what companies give on average (as days-of-pay).

Not that extra cash excuses such behavior, mind you.