Windows Server and Windows Desktop don't use the same OS? What definition of Operating System are you using here?
They have the same system libraries. They have the same kernel, albeit optimized and configured differently. They support the same APIs, run the same applications, use the same drivers, support the authentication engine, support the same UIs and shells, and use the same package delivery systems. There are differences, but I've yet to see any technical reason why you couldn't turn a Server edition into a Desktop release or vice versa.
As a counterpoint, the Ford Mondeo (4-door/5-door midsized vehicle) uses the same platform as a Land Rover Range Rover Evoque. They have the same frame, many of the same components, and otherwise take advantage of factory line construction and economies of scale. However, in this case, you could at least argue that they have different 'Operating Systems' -- they have some differences which are arguably just optimizations and tuning changes (handling characteristics, consoles, etc.) but others that are physical differences (Seats, load/capacity, etc.). You don't see Ford running out to split the Platform, though. Why? Because it doesn't make sense. There are more things in common at the core than are different, and they can make more products at a lower cost by sharing the core of the car platform. Ford has a dozen or so active car platforms, used by different models across their various brands; most other car makers do similarly.
The author is making one of several possible basic errors.
1) They don't really understand the definition of a Linux distribution (e.g. RHEL v CentOS v TurnKey v XUbuntu v Arch v etc.)
2) They don't really understand the differences between Windows Server and Windows Desktop
3) They don't really understand the definitions of the Linux kernel, GNU/Linux, and the Linux OS
4) They don't really have a grasp of how software is made or how source code is shared
5) They weren't loved enough as a child and are desperately seeking attention.
This is like saying we need to create different compilers for AMD and Intel chips, as they have different architectures. It lacks understanding of the problem and understanding of how to address a solution.