I was surprised that the article didn't comment on the wording of the slogan in the PayPal button. The words 'safer' and 'easier' are comparative adjectives; they create an implied recommendation for PayPal against other options, which are both less safe and less easy. The other buttons don't acknowledge other options -- rather, they merely emphasize speed: 'now' and 'fast'.

If you were a naive online shopper presented with multiple payment options at checkout, with no other information to guide you, you very well might choose the one that is labeled 'safer' and 'easier'.

(And it's worth pointing out that many people don't have a clear idea of what's going on when they click on any of the buttons. It's perfectly plausible that people will parse the PayPal slogan as a recommendation. Think of the infamous Facebook/ReadWriteWeb login incident.)