[Konon]

Main reason is cause if the skinner to not restrict his image itself it could overlap other skin elements causing maybe a not very good look on some actresses and general skin view.
But if he rerstricts the image window (in width) some actress will be very much shrinking!? (don't know thats the right word) but causing also not a very good look in skin view.

In this way the skinner can say when choosing a 2:3 image aspect ratio it's the perfect compromise. This problem concerns not much actresses, maybe 10 or max 15.
What do you think? 

I completely agree with this decision. A standard should be for all media. This is convenient for both skinners and ordinary users.