I see your point, but also that of the parent post. Is losing salesrank of a novel over the weekend (a holiday weekend no less), really a boom-or-bust kind of thing? If he'd been more malicious with this then this would be a crime with actual victims, but in this case I just can't reason through it enough to believe that.
How many customers did Amazon lose this weekend that will likely never hear that this was a hack? He directly and irreparably harmed the reputation of a company, how is this victimless at all?
He may have hurt the reputation of Amazon, but not through his crime. Publicizing vulnerabilities in Amazon's ranking system is what may hurt Amazon's reputation. The "crime" of messing with Amazon's system didn't hurt Amazon's reputation let alone their website much at all.
If you walk into a bookstore and steal a bunch of books, even on a slow business day and it causes the store/publisher/author to lose sales, but not that much, is it a victimless crime?