I can't answer your specific question, but Europe is funny. In particular, some routings are far less expensive than others. As has already been suggested, trips ending in London tend to be less expensive than those ending somewhere else - and fares within Europe are quite cheap. Also, fares out of JFK tend to be much lower than fares from ORD or DFW. I'm looking at a J class fare of $2 K from JFK to LHR - and will buy a separate ticket to JFK. This won't work for everyone, but is worth looking at.