Playing devil's advocate here: most websites are generated by programs, so it's possible it could be a coding error. That said, for it to plausibly be a coding error in whatever generator they're using, they'd have to store the Constitution with each paragraph in a separate file. That's the only way I could possibly see a "coding error" exclude the stuff that was excluded.
Edit: That is to say, obviously it is not a coding error. The text of the Constitution would be stored in one file because 1. that makes sense, and 2. storing per paragraph would add to overhead. And stuff in the middle of files doesn't just get deleted by a coding error.