I think that those responsible for getting this commercial banned completely missed the point.
This commercial is not "gay positive" (or whatever you want to call it)--if it was, they wouldn't be calling that man "mum,"--after all, we all know in the year 2008 that it is incorrect and inappropriate to refer to a gay man as a woman. So, if we were to take this commercial at face value, it would be reductive and derogatory towards the gay community.
However, I would submit to you all that not only does this commercial not endorse same-sex couples, it does not even depict one. Rather, in a surprisingly sophisticated bit of visual rhetoric, the advertiser is suggesting that if a housewife (the primary target of advertising for home products, mind you) purchases this brand of mayonnaise, then her sandwiches will have the same appeal as those of the fabled New York delicatessens. And, since this connotation is made in a humorous manner, the advertisers get a double whammy in terms of emotional impact. By substituting a deli owner for the mum, the commercial makes a clever appeal to ethos, and by doing so in a funny way, it makes a clever appeal to pathos (along with the traditional appeal to pathos of a mother's concern and care for her family). All in all, a rather effective commercial, I'd say... and nothing polemic about it at all.