Not seen the recent MedLife (and it's not monthly, think its tri-monthly or seasonal or something) but surprised it doesn't mention Connect out of MAN. It's been this way for a long time now and there are no plans to change it.
GB would love to offer BAConnect services and Buy on Board from LGW too, but have had their requests turned down by BA (as perhaps it would compromise the Mainline product?? not sure of the exact reason why)
Even better would be to operate a hybrid cabin with Club at the front and Connect/Buy on Board in Traveller, i'm sure this has been looked at too and i'm sure GB would love to do this and benefit from the additional revenue like other competitior Low Cost/Charter airlines but they are constrained by the Franchise agreement which so far makes this impossible.
I also agree that a Club/Buy on Board hybrid with suitable advertising and 'upgrade to club' offers would sell well out of Manch, and i'm sure that KH knows this too.... but GB can't do as they please it has to be in agreement with BA and the Franchise.
And to answer your question about advertising - thats all contained in the Franchise fee so BA take care of the majority of it. Indeed you often see GB only BA adverts to their destinations in many national newspapers now. Along with a huge promotion and advertising of 'Upgrade to Club' at LGW.