They're trying to appeal to bigger women, but IMO they're doing at all wrong, size 16 does not equal big or "fat"
If the advertisers want to appeal to real women then they need to stop airbrushing, you want real women, look at that ginger bird from Corrie, Fizz I think her name is, or that lass who plays Ugly Betty, yes I know they have tons of make up put on them but my lass is a size 16 and she doesn't look like that lass in the photos at all. (She doesn't look like Fizz or Ugly Betty either but thats not my point, they both have stomachs on them)
They won't ever use "real" women that you seen walking round the high street because, just like the cosmetics industry, they're trying to sell hope.
Basically that advert is saying:
"Look this lass is a size 16, if you're a size 16 too, then buy this stuff and you could look as good as she does"
When in reality it's saying
"This lass has had a ton of make up and airbrushing, if you buy this stuff you won't look like her, but your other half might actually pay some attention to you if you buy it"