I can't imagine anyone wanting the hassle of a Euro hub connecting flight followed by hassle, followed by a flight of 8+ to get to NYC when they can do it non stop in a fairly low density 757 with 31" in United Economy and 37" in UE+ which is comparable to their 777.
I've never understood this notion of two aisles being better. How often do you use two aisles? The crew usually do their service at the same time so both aisles are blocked simultaneously for those who INSISIT of using the facilities during cabin service.
Another benefit of a smaller jet is there's less of a surge toward to the border on landing versus up to 400 on a wide body.
757s across the atlantic are here to stay and without them this route would not work. The 757 issue has been done to death and I'm bored to tears with it. This flight gives people choice. They can choose convenience of they can trail to LHR/AMS/CDG for that elusive second aisle whilst still getting the same service, legroom and probably paying more for the Priveledge. Each to their own.