Face shape is the most evident. This is a photographer oriented post, you may have to look longer and harder to see the same things that a trained eye would immediately notice (same with graphic design).
The cover is not intended to be analysed in great detail. It's wholly a subconscious process.
And certainly narrowing a jaw slightly will be aesthetically pleasing on a woman.
Think of it like a slightly out of tune piano key. Used during a single song. Is it really noticeable? Not to many, will it be a better recital if it was intune? Certainly.
Maybe?
Doesn't what's aesthetically pleasing change from person to person? For instance, I don't find most people on magazine covers to be all that aesthetically pleasing -- but I am also aware that there are many who do.
Our experiences in the human world are shaped by millions of tiny, and often invisible design decisions. We could surmise that a decision is invisible to us and thus meaningless, or we could practice a bit of humility and attempt to see and understand what work was done there, and how it affects us.
Isn't that the exact point of the change, to increase value to potential buyers? These aren't magazines for experts.