Phones and tablets are not PCs
The assumption in this article is that MS has to succeed in the phone space.Yes the decline in the PC market is partly due to a certain class of PC user finding a new class of device that fits their needs better. This is a fragmentation of the sector into two markets. Just because people used to use horses for travel and the plough does not mean the future belongs to a unified tractor-car hybrid. Tractors and cars might be made by the same company and use the same basic technology but its not the same product. Apple does ok making a phone and computer the same way Honda does ok making tractors and cars but they are different products. Not every car/tractor manufacturer has to make both and nobody succeeds with a unified solution even if some of the parts are the same. In fact market fragmentation is better for business because apple can sell you a phone and a laptop if you need both.
Phone/music-player/camera combination seems to work as a combination because they are all portable devices you want to carry around and separate devices would compete with each other for pocket space.
Microsoft can't seem to do phones. Apple have never done much in the games console space they both compete in the PC space. Once upon a time Microsoft managed to expand their market by making windows a server as well as a desktop OS and this has resulted in a fetish for using windows as a solution to every problem. Its not.