AA did it to have a rolling "bank"-sorta thing going on for flight from North Carolina to LHR. So:

6:00ish US730 CLT-LHR 333
8:00ish AA174 RDU-LHR 763
10:00ish US732 CLT-LHR 333

I guess it was so CLT-LHR and RDU-LHR don't clash and/or make it more convenient to have flights from NC-London every two hours between 6pm and 10pm.