Personally I'm very surprised that my first thought on the Xena one was get up. The spine's the same, the ass up is the same - though it's covered. Maybe it has something to do with Xeam = Strength to me.Look at Conan and Storm again. The most prominent part of each picture is the exposed left buttcheek, there's also a good central view of her exposed back and a little bit of the side of her breast. The first thing you notice in the picture is the exposed flesh and that sets the tone of the whole image.
But I don't find it gratuitous. I just go "Xena Get Up!" and worry about the bad guys and who was strong enough to do that to her.
With Xena, her plain leather skirt covers her butt (it falls just perfectly to) and her breasts are fully covered, and the what stands out is her armor, not her flesh.
Superman is drawn the way his costume normally is, covered up with a shiny uniform. Not particularly provocative.
Every part of a piece of art is important, because the artist is trying to set up an overall mood. Every line in the drawing needs to support that mood somehow. A piece of superhero art is supposed to evoke a sense of heroism, even when the character is flat on their face. You are supposed to look at it and be impressed with what knocked them down, and ready to see them stand up in the next panel. That's what a cover image should be. Its supposed to make you want to pick up the book and look inside to see who they're fighting and how they kick the bad guy's ass after being thrown so badly.
When an artist focuses too much on making the subject of the piece look sexy, as Larocca (arguably) did with Storm and Bellatrys did (purposefully) with Conan by put so much attention on bare flesh, they destroy that. If the viewer's eye is first draw to a titallating image of a character's butt and thigh, you've lost the chance to make them worried about anything other sex. The viewer is not thinking about how the character got to be face-down on the ground, the viewer is focusing on the character's butt. The viewer is not anticipating that this character will crawl to their feet and punch the bad guy in the face, the viewer is thinking about the possibility of even more exposed flesh. Its not a matter of femininity or masculinity so much as sexualization period here.
This is one of those points that subjective, some people might not think that Storm in particular is a distracting amount of skin (comparatively, it doesn't seem like a lot except that her butt is the focal point of the cover) and its certainly not the worst cheesecake I've ever seen but its a good example of an artist slipping over the line and losing the desired effect. Its not just that its unnecessary, it is actually harming the overall image by screwing with the artist-viewer communication. If you go out of your way to draw cheesecake you lose a lot of the drama superhero comics are supposed to give us. Pinups are one thing, a cover scene like this is another. (Interior artwork is the worst time to be cheesecakey at all, because then you are interrupting the story itself by distracting the reader, but that's another complaint entirely.) The cover is supposed to make me want to buy the book. I'm supposed to look at that on the rack, get worried about what they'll do with Storm (granted that image makes me worry about how they're handling Storm but not in a way that makes me want to see what they're doing to her) so that I'll pick it up to see who tossed her and how she gets back on her feet.
The bottom line is that in a visual medium too much sexy can hurt the story. Artists need to be more thoughtful about what they put in an image.