One could speculate ad infinitum, and that is part of the learning process we all go through.
Perhaps, early on, IDIX thot they could replace ribavirin w/ NM283 and in early 2006 they were thrown a major curve with the GI effects @ higher doses. I dunno. JP does seem to be hedging more lately (last CC) in mentioning use of 400mg dose and speaking of the differences in SVR Europe and US populations.
This is the first time i heard him use the "magic" word for ribavirin, but as i understand it, its mechanism of action is not well understood.