At first glance, these stats almost seem wrong, but when you start think about it, they make sense: The survey polled "households," which, on account of grandma's Compaq or your roommate's gaming PC, clobbers the exclusivity figure. (I live in what any reasonable person would call a "Mac household"—three people who use Macs almost exclusively—but that little Acer netbook sitting on the table means we're not.)
Plus, PCs are cheap and they linger, and Macs, being pricier, tend to find their way into richer households, where more than one computer is almost a given. That, combined the fact that most Macs sold are laptops, and therefore a little more likely to be a supplemental computer, makes the 2% figure look a little less crazy, but still, 2%? Fanboys, you're slacking.