Not completely true. If you get fired, you have a month to find a different job. Of course, the issue is with finding a different job that is willing to jump through the hoops involved in letting immigration know that you are now working with them, but there are plenty. Problem is, of course, that knowing that you are dependent on them, some companies will give you worse conditions than a resident/citizen with the same skills would have, especially as far as the salary is concerned.