Not necessarily of the type offered by US airlines. Some of the most profitable airlines in the world (like SQ or QF) will only upgrade if you either pay for the fare difference in cash or with a fistful of points, regardless of your status. Relationships are cultivated with frequent flyers though the quality of the economy product, access to lounges on domestic travel once you reach a certain tier etc, rather than through giving away the fare differential which could be one of the things lying between profitability and Chapter 11.