In an article at printmag.com, design artist and critic, Steven Heller, claims that the cutoff-torso-spread-leg framing device is possibly the most frequently copied trope ever used. In fact, Heller calls it a "design virus"; one that persists to this day. He names it the "A-Frame".
As usual, I couldn't leave well enough alone, and had to start dissecting the reasons why this is so prevalent.
According to one source, "a woman’s legs in the A-frame position usually connote domination and empowerment over a puddle of males, and lots and lots of sex". Sounds reasonable enough - you don't have to think too hard to arrive at the conclusion that a close-up of a faceless woman's legs, spread apart, must have some sexual connotation.