Laptops running Windows make up more than 1% of the PC market. MS aren't just pitching to replace the hundreds of millions of ten year old office PCs running XP.
By 2015, the percentage of Windows laptops sold without a touch-screen will be single figures, as the differential between the cost of production diminishes and manufacturers compete based on value-added features.
Watch the TV ad for Windows Surface Pro. A boss buys his entire staff a tablet, so they enjoy a 'fringe benefit' of a lifestyle device outside work hours. This tablet also docks to a keyboard, so that they can run standard business programs; a free gift of a convertible tablet enslaves the corporate user to be connected to the workplace 24/7 - evil genius.