I'm a bit surprised that software isn't higher on the list, since it's the least tangible of the goods compared and often comes only in a form of a download link.
Also, the article doesn't mention how exactly the data was compared, but it looks like it took into account the number of transactions, rather than the amount of money spent, or else electronic items and airline tickets would be higher in the rankings.
I guess as someone working in retail I should not admit it, but in hopes my boss does not frequent this forum I will: I am a big online shopper. Not only don't I have a car (so having everything delivered by the mailman is simply more convenient for me), but more than anything else it is just so much cheaper. And if you use cash back sites, it becomes cheaper still. Just within the last week, my online purchases have ranged from a 90 cent pen to a $950 laptop. If I were to total last years purchases, the categories I spent most money on would be photographic equipment (I guess that would go into "electronics"?) and travel. In terms of the number of purchases, probably photo equipment would win, too.