All this means is there will be one operation system for "Windows Phones, ARM-based Windows tablets/PCs, phablets". Don't know why the author included phablets. This just a big Windows Phone.
This comes down to one operating system for Windows Phones and ARM based tablets, the touchscreen devices. The Microsoft Surface 2 and RT are the ARM processor devices this is referring to. Microsoft said last year the Windows Phone and ARM Surface tablets would eventually have a unified store for apps and this will start with the next phone update and the next Surface update.
This is all about decreasing the number of operating systems. Right now there are three. When this is complete there will be two. It has nothing to do with desktop or laptop operating systems.