Mobile devices like smart phones, tablets, and other "portable media" devices do not share the same hardware nor the same capabilities as a "real" PC, no matter what marketting and commercials try to tell ya.
A "real" PC needs a number of features that mobile aps do not. Functions that are necessary to use an iPad, for example the touch screen interface, are clunky, and intrusive on a PC menu screen.
The system requirements, the hardware overhead, the drivers themselves for the minimized mobile hardware, nothing amongst the two categories even corresponds on a 1:1 scale to the other side.
Please support the argument that they SHOULD have the same OS? Because that is not logical. I'm not talking laptops, either. I lump those under "real" PCs.