Parabellum you are right on the money!
If everyone took the selfish attitude of previous postings then the industry would collapse or people like Ryanair would prevail whereby you must pay for your rating, but the management can sack you if you fall out of favour with them - I am sure nobody wants to feel this vulnerable!!
A contract is a contract. By breaking it, you will not only make life difficult for yourself later, but stuff it up for any new people joining your present company.