To be fair, very few other racy pictures of women have been canonicalized like that, either; about the only pictures I can think of are paintings, specifically the Mona Lisa, which is hardly racy, and Boticelli’s Birth of Venus, which I suppose you might look at as racy, though I wouldn’t particularly. There’s a couple other non-picture works of art that are canonicalized in that way, but aren’t themselves pictures – Michaelangelo’s David as mentioned in a sibling comment is a good example. But then, even though the canonicalization makes them into something else, it is usually based on upon perceived artistic importance, the Lenna is a different and arguably sui generis phenomenon.

If you had a point, you wouldn't need to behave this way. (As opposed to some other people who disagree with me in this thread, who do have a point, and don't feel compelled to do this.)