Maybe it's the irony? I don't know. Susie is a bright name, if you think about it phonetically, it's sue-sie. Your voice goes up when you say it, thus why I describe it as 'bright.' There's no depression in the pronunciation, it's almost child-like. For me, at least, it evokes pictures of innocence, which is why "Little Susie" is such a powerful song--it's the destruction of innocence. It wouldn't work quite as well if it was "Little Darla", or "Little Olga." I know I'm probably not making any sense, but that's what I think.
As for "Superfly Sister", it seems to me as though Susie's the one who's abstaining from 'doing it,' since she's keeping Johnny "on his knees," "getting the boy and making him wait," etc. She, and Mother, seem to be the counter to the promiscuous Brother, Sister, and "He," who seems to be a predatory creature and possibly a danger to Susie. That supports the Susie=innocent hypothesis.
Blood on the Dance Floor is, of course, the exact opposite. In this song, Susie is the predator and not the victim like in the last two songs. Again, though, as the song's title implies--it's not a regular scenario. People don't expect to find blood when they go dancing, nor do they generally associate dance floors with murder. The dance floor is generally seen as a positive thing, a place to have a good time, so to stain it with blood and murder would be to tarnish it, in a way. Thus, the Susie in this song can be equated with the dance floor, because she's been 'corrupted' by her predatory nature. She passes herself off as a good thing, as a "friend," but is in fact a wolf in sheep's clothing who murders the men she seduces. The name Susie, then, is still one associated with innocence, even if this particular Susie is anything but--she uses the name to hide her image, a false front of innocence. Not many grown women, after all, tend to go by 'Susie.' By the time they reach adulthood, they usually stick to 'Susan', or 'Sue', to project a more adult image and distance themselves from their childhood self. By choosing to go as 'Susie', the woman in this scene is projecting a more innocent image. We can deduce she is at least 18-21 years old, because that's generally how old one has to be to go dancing at clubs.
Furthermore, Susie is actually short form for "Susan." It's not a real name, but a nickname, usually given to young girls, as I said. The meaning of the name "Susan" is Lily, a flower most often associated with purity (especially white lilies) and death. In pre-Christian times, Lilies were associated with sexuality (we could see how this could tie in to both SS and BOTDF.) However, in the Bible and Christian theology, Lilies are a symbol of purity, and we could see how that would be important for Little Susie, and even Superfly Sister, since the latter song is about sex and the loss of purity.
lol
