Sadly, pirates don't actually convince their friends to buy it. They help them pirate it. He's right about doing what he can to provide features that pirates can't take advantage of, though. That's the only way to actually combat piracy.
Now 6 of my friends (who never would have been hooked on the series otherwise) own legal versions of the two most recent novels starring our favorite wizard-detective.
Those sales would not have been made if they hadn't gotten a taste of the series beforehand. Sure, this situation isn't the rule, and they pirated 5x the books they've purchased... but 2 sales each is better than 0, and with 8-10 more books coming in the series, the author/publisher have come out far ahead.