http://www.itv.com/news/update/2014-11-14/sainsburys-selling-5-000-british-legion-chocolate-bars-per-hour/
And at least some of that will be new customers, many of whom will buy other things whilst they're there.
Building their brand
I suppose you are right Igor. Sainsbury's will be building their brand as that's the purpose of advertising. And there will be a donation for Royal British Legion.
I still don't have a problem with the ad. I would have had a problem if the soldiers had been all singing and dancing brandishing Sainsbury's merchandise and entreating us to shop at Sainsbury.
As has already been said Paul McCartney used the same scenario back in the 80s with his Pipes of Peace song and he would have made money from that. Same with Jona Lewie with Stop the Cavalry. Blackadder goes Forth would have made money too for its writers and actors.
This is just my opinion of course.
Funnily enough I contributed to a previous thread earlier this year where someone was pondering if Dad's Army was disrespectful to the memory of those who served in the Home Guard. Some contributors said it was and their late fathers/grandfathers who had served in WW2 hadn't watched it for that reason. Others said there was nothing wrong with finding humour with that situation. I commented that I had felt even in the 80s uncomfortable watchin 'Allo 'Allo - with mixture of SS, Gestapo, French Resistance and British pilots- it had never seemed an appropriate subject for a comedy to me. But others chipped in saying that laughing and finding humour with past events was acceptable and I believe one person said it "was what we British did".
So I suppose it's all a matter of personal opinion.

Looby