This has been raised elsewhere -
ads. by definition offer a distorted view of reality because they are designed to draw attention to the product(s) involved.
The idea behind the M & S campaign is that all the ladies admire each other's (M & S) outfits, inferring that wearing such clothes will garner the approval of your peer group, and make you feel attractive.
It don't think it's weird - any more than any advert is weird - they are all designed to stick in your mind - so this one has succeeded.