we had an interesting discussion about this very topic in my Race and Gender in Media class this morning (i'm a journalism major). Our prof showed us some of Dove's commercials and asked us if what they were doing was responsible.
my opinion is this: advertising is inherently manipulative; no matter what, they're trying to appeal to a portion of our psyche and convince us to buy their product. the argument against the traditional images of beauty in advertising is that it made products (beauty products in particular) aspirational and attempted to convince women that there was something intrinsically flawed with their own appearance that needed fixing. if you bought their product, you could fix your flaw. Dove's campaign is different (and i think a little patronizing to women) because it appeals to womens' desire to see images that reflect themselves, but Dove still wants the same reaction out of you - instead of saying 'here is what you could be, here is a product to fix your flaws' they're saying 'here is what you are, flaws and all, here is a product to fix your flaws.' i find it a tad condescending, honestly. instead of using someone flawless to sell the product, they show someone flawed, but the implication that we all have something about our physical being that needs to be 'fixed' is still there, and that's what women should find insulting.
the over-40 model search that you bring up is a little different because they're not selling beauty products, imo. i find that very admirable. they don't imply that the over-40 models need to be fixed, they're celebrating nontraditional images of beauty.