Agree 100% with Shed's comments.
I further suggest the catalyst for the DL/VA moves is that LHR is full. Possibly these two airlines are coming to terms with the fact that they are not getting any more LHR slots for at least another 10-15 years, and only then if/when R3 is built. Therefore between them they need to :-
(1) squeeze as much profit out of their current LHR slot holding as possible (because they ain't getting any more !) and
(2) look beyond the LHR perimeter fence if they want to grow their alliance and their share of the UK/NAtlantic market. LGW is too close to LHR (they've both been there, done that), so they can only look elsewhere. MAN has a huge catchment, good and improving surface links, and two under-utilized runways for large swathes of the day. Maybe (just maybe) the penny is starting to drop in a few airline boardrooms !