I had an interesting time at the Seattle PASS conference a few years ago getting some of the Microsoft geniuses behind SQLOS (who insisted that the memory allocation process responds to memory pressure and no max memory setting is necessary) and some other Microsoft geniuses that insisted the other group was nuts. It was very entertaining, but inconclusive.
I would put more faith in the opinions of real-world users, and go with the 12GB recommendation.
The conference is in Seattle again this year but I can't attend. Maybe someone else can get a straight answer.