More specifically, the source blames PC makers' "inability to deliver," extremely strong words that completely justifies Microsoft's move into building their own hardware, the Surface.
Additionally, the software giant has been looking to expand their Microsoft retail stores, which could put them in even bigger competition with their hardware partners.
Another potential reason for the slow sales is the confusing different versions of Windows, most notably the Windows RT seen on the Surface tablet. There has been widespread confusion on the differences between RT and the upcoming Windows 8 Pro. RT can only use apps built for RT, unlike Pro which can run on AMD or Intel chips and has access to the hundreds of thousands of Windows legacy applications.