I personally think that JB was abused, however, I do believe that the hymen can be broken by everyday activities such as bike riding, vigorous exercise, etc.
I saw this on a 20/20, Primetime, etc. news type show a few years ago. They were talking about how Pakistani/Middle Eastern women were undergoing hymen repair surgeries to make sure they had an intact hymen at their wedding so that they weren't beaten or murdered if they didn't bleed upon having sex for the first time. Apparently, it is custom for the men in this culture to display the bedsheet with a blood spot on it as proof of whether the woman was a virgin or not. This show's featured doctors also said that most American girls broke their hymen at much younger ages due to the difference in culture where they participate in sports such as soccer, gymnastics, etc. and that it didn't have anything to do with virginity. I also believe the Dr. 90210 show touched on this subject once. I don't watch that show, however, so I don't know if it said anything about young girls or just the one having the surgery. Just saw something about a hymen repair on the preview clips.
Sorry, I don't have a link. I saw this show a long time before I started lurking at this site.