A fairly good article at Gamasutra, with links to some other articles about the improbability of female armor as depicted in a lot of fantasy. Although the article is focused on video games, I think it has applicability to fiction, particularly to cover-art for novels, graphic novels, depictions in film, and so on.
Gamasutra - News - Opinion: Video games and Male Gaze - are we men or boys?
Gamasutra - News - Opinion: Video games and Male Gaze - are we men or boys?