MercenaryAli is showing his ignorance here. Why add to the risks inherent in an engine-out approach (with the assumed engine-out go-round) by attempting it at MTOW? Never having flown a 747 (or any other Boeing) I don't know how close to MTOW this aircraft would have been, or the difference between MTOW and MLW; however, I suspect that to reach MLW a significant amount of fuel would have to be either dumped or burned off. If you have fuel to spare, and no immediate risk (even if a second engine fails), why not use it to continue towards destination?
At the very least, the decision to cross the continental USA seems sensible- use that fuel to take the pax closer to their destination, reduce the risk involved in the approach, and give the company time to prepare engineering support at a suitable airfield. Should any further problem have occurred, there would have been a multitude of potential diversion airfields available within a very short distance of track.
The decision to cross the Atlantic is more of a surprise to me. However, as BA probably has more experience of operating the 747-400 than any other operator in the world, I do not feel qualified to judge that decision- especially as in this case, by the time the aircraft reached the eastern seaboard of the USA, any further incident can be considered extremely unlikely.