My explanation for that success was that people were buying netbooks and then opting for a desktop + netbook combination rather than netbook + laptop (which seems redundant).
I think we'll see a similar effect when iPad sales kick in - the combination of an iMac for the home office and an iPad for the rest of the house and out and about seems like a winning combination.
In my house I've got a Mac mini in my office with it's own monitor, another mini attached to my living room TV that hosts most of my media (photos, music, and some movies). I have a couple of old Windows laptops that I use around the house or out and about. I've been holding off buying a new laptop to see what the iPad could do and it seems to be a good fit for my needs.