I think some of it also comes from the ideas of 'masculine' vs 'feminine.' In terms of the DRK pose, which seems to be the most brought up example, it appears 'more manly' to have a massive sword slung over the shoulder, held with one hand. It's a display of strength. For a female, having it downward in the ground held with both hands is less aggressive (as in, "manly") and more defensive. To be honest, the male pose (as boring as it seems, and yes it's Cloud's) makes a dark knight look aggressive and dangerous, while the female pose puts emphasis on the 'knightly' or 'defensive' ("Tank") side of it.

That said, the ideas of masculine vs feminine have gone out the door since they gave the bunny suit to males. I don't see a point of gender-locks on job specific poses, as long as it stays to the job.