Everyone is assuming that BA were actually making money out of handling ASW's flights at Gatwick. Knowing the costs of the Gatwick operation, it is by no means a foregone conclusion that it was making money - it all depends on how you look at allocating bits of cost to different bits of the network!
I would have thought that BA would also be happy to get ASW off their check-in zones given that they are being "squeezed" on the numbers of desks they have at Gatwick from when Continental move into North Terminal from July.