What would have been wrong with making win8 a DIFFERENT product?
Other companies have all sorts of different products. Just continue to support Window 7 and introduce a NEW product that is NOT backward compatible. It's what they're going to have to do eventually anyway.
Because the tiles are inefficient on devices without touch. Takes too many steps to get to one's W7 apps. W8 apps push paid adds to your OS and because basically it forces a tablet-smartphone user and business model on PCs served better by existing OSes.