Before photography and boudoir or art nude photography, there was drawing and painting of the nude. The human form, especially the female's has been a subject of art for hundreds of years. Even when the strictest of morals was in place, artists still could depict the female form in their artwork. Now, whether or not their model was an actual female is another topic. During Michelangelo's time, women could not pose nude for male artists.(Similar to Shakespeare's time when only males could play female roles) Ever wonder why the women on the Sistine Chapel have biceps and pecs? He made up the female form based on a male model. But I digress.
I think if you Google'd famous painters that you're familiar with, you would invariably find a nude they've done during their careers. Was this boudoir? Burlesque? Art Nude? I think what is fascinating is that the photography of contemporary women for their personal boudoir session or an erotic nude portrait is just on the continuum of art and all those female nude bodies that came before them. Photography is another art form that is more readily available, a little more cost effective and can be made permanent for posterity. Will they end up in a museum? Doubtful, but I think we cherish our portraits like a piece of artwork. And they're you and not some 18th century female staring back at you!