He was asked to comment. Which he did.
And so JK Rowling will lose book sales to devout Catholics that read about Benedict's remarks, and gain sales from non-Catholic's annoyed with what they consider to be his meddleing.
I don't think sales numbers are going to be a problem for Ms. Rowling.
Hmmm... selling Harry Potter novels to kids whose parents won't let them read it... sounds like a great black-market opportunity to me...
(Kidding. I respect parents' rights to rule their kids' lives absolutely)