Has US adopted that? The US site still says:
As long as you booked your flights together in one itinerary, we'll check your bags through to your destination. We'll also check your bags through on all of your US Airways flights.
If you have 2 or more tickets that you booked separately, you'll need to pick up your bag and re-check it with the next airline.
I know that US stopped checking bags through unless it was all one ticket - something to do with the recent DOT rule about collecting baggage charges when more than one carrier was involved.
Jim