Fundamentalist Christians explain why here: "Did Adam have a belly-button?" from ChristianAnswers.Net [I owe full credit for this hilarious link to Pascal Riché in his "Le ventre d'Eve" entry in the blog "A l'heure américaine".]
It seems to me that I had an illustrated Bible as a kid in which Eve most definitely had a very cute belly button. I don't know which Bible Mr. ChristianAnswerNetMan has been reading, but I have a fundamentalist's faith in the nude images burned into my brain as a child.
-true blue liberal