All Star Alliance partners of United are not equal in terms of earning United RMs or EQMs. USAir is great in this regard. If you are United elite and book USAir you get the same RM bonus as you would as if you booked United. If you book premium class (not simply pay for an offered upgrade at check-in) with USAir you get the bonus United EQMs. Also USAir gives you priority boarding based on United elite status. I don't know why USAir does this but it certainly induces me to fly USAir in preference to other Star Alliance carriers when United does not offer a convenient flight.