DL JFK on 763 @ 199 seats.
BA JFK on 763 @ 189 seats which changed late last year, I think.
Either which way, BA were operating with 213 seats last year on dear old 'WH and so the reduction of 48 sector seats per day x 30 days means that a maximum of 1,440 customers could have been lost due to this cutback if BA operated at constant 100% loadfactors (which I doubt!). The CAA stats show over 6,000 fewer passengers between MAN and JFK in June 2007 than June 06, so the issue is far more fundamental than a bit of capacity reduction by BA.
It also can't be said that it is the effect of LPL-JFK. CAA stats show 2,575 passengers on this - which (if they actually flew the daily service planned) means 43 passengers per flight ex Liverpool. Uugh.