There may be some more room soon in T3 if American Airlines continue with their pricing policy.
Looking at random Man Jfk flights in June, it is considerably cheaper to fly via Lhr than to use the direct flight.
Before anybody says that it costs more to use a non stop flight, I bet it doesn`t apply in reverse i.e. I bet it is not cheaper for a Lhr passenger to go via Man than to use a Lhr Jfk non stop.
I have not looked at Man Chicago flights but I bet that the same principle applies.