FYI-
I have almost 6000 hours in the Airbus 320 family of aircraft, many of which were acquired in transcontinental flying. And in that time, I have only made ONE technical stop for fuel. And that was owing to an extraordinary jet stream with headwinds in excess of 140 KTS for much of the flight.
The company uses the A321 transcon because it costs less to fly it than the B757, and it only carries 8 fewer passengers than the B757, as both are currently configured.
Not to mention it is a more comfortable airplane for crewmembers and passengers alike and has better inflight entertainment systems.
Happy Flying.