First, we'll consider only hardware equipments and not OS's:
If A produces a part P that he sells to B, who then puts that part into a bigger thingy which he then sells to the public, then when people refer to the OEM of that part P, they should be referring to A.
The OS's part (well, I'm only discussing Windows) needs to be discussed separately:
Microsoft, overall, has two licensing versions in which they sell their OS's:
1. Retail: This is the one intended for consumers. It's nicely packed in a pretty box with documents and stuff. Since the OS is not being sold by MS for the intention of…