Unfortunately JCoure it doesn't seem that you understand much about these visas.
The people you often see at convenience stores are here on student visas which permits them to work a certain number of hours a week. Where someone has a skilled visa, they're typically on what's known as a "closed work permit" where their visa is bound to working for a particular employer for a certain period of years (sometimes 3-4) till their permanent residency is processed.
Once they're granted rights to permanent residency they're free to do what they want.
