Aren't most Playgirl readers male?
If true, this would be an interesting explanation. Perhaps men are the driving force behind
both stereotypes of women and of themselves? However, it sounds like these conclusions are based off multiple sources and not just their centerfold study (several other concurrent studies are cited in the article). I'm not sure if this explanation would apply to all examples or not.
Scientifically, women like men who are larger because it means the male can protect them. In reverse, I would think men would like women whom they can protect.
It's also a social status thing. Heavier women used to be richer. Now it's the opposite.
Standards of beauty are entirely a societal concept.
I think this is the obvious explanation (although that doesn't make it right). The question then is why we're moving
towards distinct gender roles in this case, rather than away from them.
Put differently, there are lots of ways for women to be dependant upon or "protected" by men. They can be protected/dependent economically (i.e. the man provides the money / resources), they can be dependent intellectually (i.e. the man makes the large, important household decisions), they can be dependent politically (i.e. women do not have the right to vote or customarily vote however their man does), they can be dependent emotionally, or in any other number of ways.
And in almost all these ways, we have made significant strides towards equality between men and women, where women are no longer protected by / dependent on men. They are much more independent financially (wages for women have gone up over time, there are more jobs for women in general), more independent intellectually (women are advancing much further in high education), politically (obviously women can vote today), and so forth. While we aren't perfectly equal yet by any means, we can see ourselves moving in that direction over time. So why are we moving away from men as the stereotypical protectors/providers economically, emotionally, politically, and intellectually, but moving towards this stereotype physically?