Netbooks are not primary machines. They're not meant to be primary machines. Netbooks are for people who have a desktop or very able bodied laptop and want something (more) portable, but don't necessarily need something very powerful. I will exclude MIDs, UMPCs, and the new tablets coming out from the PC segment, since they aren't netbooks and would only hurt those numbers. What we end up with is desktops, laptops, and netbooks. Desktops will always hang around, albeit in ever decreasing numbers, simply because of enthusiasts. Laptops, AFAIK, are currently the dominant primary computer being sold. This is because people want something that is portable, powerful enough to run apps that used to be dominated by the desktop, and don't care as much about upgrade-ability. That leaves netbooks only as secondary machines, or for people who need a computer only for the sake of needing a computer. The former group, by nature of it's definition, cannot occupy more market share than that of desktops and laptops combined (10% by Mr. East's estimates). That leaves more than 80% of all netbooks in households without a laptop or desktop. The later group are better served by crappy laptops anyways, as much as I hate to admit it. Even if we presume that the maximum number of netbooks are in households with a desktop or laptop, and that households only have 1 desktop xor 1 laptop (ha) in addition to 1 netbook, and for the sake of easy math, any house that only has netbooks (or the disqualified MIDs and tablets) has exactly 2 of them, you're looking at 80% of households without a primary computer. That number rises sharply when households only own 1 netbook.
Maybe what Mr. East meant to say is that 90% of the computing market (ie anything as capable as a smart phone and above) will be non desktops. That I can believe, and probably wouldn't even question it if I were told that today. That segment includes smart phones, MIDs, UMPCs, tablets, netbooks, and laptops. Even if we exclude laptops, the former 5 combined make up a respectable portion of the market. But smart phones and MIDs are not PCs, and UMPCs and tablets only make up a tiny portion of the market. That essentially leaves netbooks by themselves.