I wasn't terribly surprised by this news, but apparently Marketwatch was.
Why would a dinosaur like the PC outsell something as slick, new, and impressive as a tablet? Ask any writer you know, and they'll tell you. This quote from the article probably says it best...
“Unless you’re shooting for a degree in Angry Birds, tablets are a horrible back-to-school purchase,” says Louis Ramirez, senior features writer on DealNews.com. “You can’t write a 10-page research paper with an iPad.”