Yes, it's "normal" for that part. I've never thought about why it is normal before, so it's kind of interesting.
I might just paint mine too but the rust extends up into the tube anyway. My gut feel is to leave it alone since it's not really a cosmetic issue.Thanks guys for all the information and for taking the time to take pictures of your dear ladies (or gentlemen).
Maybe in the future I will put some paint or some kind of anti rust treatment, but for now, and seeing your pictures, I don't worry too much.