BOS-LGW has done poorly for DL since day 1. There's a lot of competition on this route and DL is a late-comer. If DL intends to build up BOS (as they have said), then they'll probably keep running BOS-LGW even though it is losing money. Eventually, if DL can add more feed to BOS and as the economy improves, the route might become profitable.
BestWestern, JFK-LGW on DL would be a miserable loss. Tons of competition from UA,AA,BA and CO and DL doesn't have access to LHR. Add to that, DL's feed into JFK is pretty poor and you have a recipe for red ink.