That was the first reason that popped into my head as well. It is also a possibility that iPhone users are more comfortable with transmitting their payment information through cell towers (I do not know if this is true, but as an Android user with an aversion to "shopping" on phones I am led to speculate it at least).

Responding to the article directly: I hardly believe that the absence of shopping on a phone turns it from smart to dumb. There are in fact far more interesting activities to engage in on a phone than simply buying items (i.e. reading a book, browsing the web, taking photographs, emailing/texting, etc.)