Well, from the Gov's POV, they don't want to import wards of the state. If you arrive in a country, someone has to fund you. Tying it to an employeer guarentees that you're funded. Without that you're just filling up ERs and hostels, etc.
The parent was proposing tying permanent residency to taxes paid or something. If you've paid $1M in taxes, you've demonstrated that you're not likely to become a burden on the state.
