Why should MS decide what tablets and phones need as minimum hardware?
Not only minimum, but maximum as well. MS gets to decide the biggest screen size, the highest speed CPU that can run Windows - tablet edition, on a non-desktop form factor. MS does not want vendors selling full fledged Windows on tablet form factor devices even though it is technically feasible.
Hardware had to be compatible to sell bundled with Windows.
MS does not want to encourage vendors who also provide open source drivers with their hardware. In this day and age, if MS made a reference standard for writing drivers hat did not require any signing, many vendors would only be too happy to innovate.
MS's goal is not to promote innovation, but to restrict vendors from making PCs that can also run Linux flawlessly. Having lost the tablet and phone business to Linux and Android, MS wants to keep on stifling the Linux desktop for as long as they can. One way they do this is to give incentives to vendors that make only Windows compatible hardware. Also the driver signing and Windows Update gives them a lever to destroy any vendor who gets too cosy with the Linux world.
http://msdn.microsoft.com/en-u...
From Vista and up, the hardware can be designed to give out intentional error messages that are ignored by Windows, and thus the hardware becomes unusable in Linux.