I had the same thought. Our PPC consultants strongly recommended that we do branded ads and I pushed back against it using this same logic. Ultimately we performed a test, but the results were very different from in the article—we did find that a significant percentage of those who clicked our branded ads would otherwise click the organic results... but far from 100%. And because cost per click on branded ads is so low compared to other ads, it appears that they are still profitable for us, even once we take into account the users who would have arrived through organic links if the ads didn't exist.
This was and is surprising to me. The only explanation I have is competitors bidding on our brand keywords and taking traffic that would have come to us absent any ads. Which makes the whole thing look like a nice racket for Google. Regardless, for now we pay since the alternative is apparently to lose those users.