It is a classic example of how BHX gets continually squeezed these days by LHR to the south, and by MAN to the north.
This is very true not just with US Airways but 'Any' Airways. Apart from feeder services, if a route makes money the carrier will stay the course. If it doesn't then it will stop flying regardless which political party is in power. BHX has always been squeezed between MAN & LON. Nothing much will change even with the extended runway. Even if Management offered discounts and enticements to carriers this IMHO wouldn't even work.
Willy Walsh wants a 3rd runway at LHR and not a 3rd London airport. BA made the decision to pull out of the regions 10 years ago and they're hardly going to reverse that decision.