You know, I never knew that... But I looked at my school's program and realized that I'm earning an MS. Just an MS. Actually I never knew that there was such a thing as a real BSN or MSN. I thought it was just shorthand for nurses to know that the person's bachelors or masters was in nursing and not, I dunno, sociology or something.
Degree stuff is interesting. My undergrad degree is technically an AB, not a BA. I only know of one other university that does that (Harvard, FWIW). But I never write AB on anything because I assume that most people will think that AB stands for associate's in business or something... I usually just write the words out, because I'm kind of a stickler about accuracy and don't want to say that I have a BA if that's not actually what my school considers me to have. Yeah, I know it's not important in the grand scheme of things, but it can be a bugaboo for some of us.