I'm confused? Sinofsky said at Build that there was 450 million W7 PC that were W8 ready. Does that mean they're all getting denser LCD displays included with their upgrade to W8? A big LCD panel giveaway? IMO Microsoft is saying "F the old PCs. Just deal with it". Microsoft is counting on the fact that PCs will keep selling and those PC will always ship with the latest version of Windows no matter how badly they cripple it.
Just because older W7 PC spec hardware is capable of running W8, doesn't preclude the introduction of newer W8 spec hardware which will be even better. Indeed W8 goes out of it's way to adapt to older hardware in more ways than just cleartype and high dpi support, such as enabling special support for the less sensitive touch displays found in W7 devices.