Well to be honest with you, I could not say whether a judge has or has not ruled on this. I don't study Law and I find it incredibly boring ; - )
You should talk to the individual software vendors and / or hardware vendors for further accurate information in relation to thier respective licensing agreements. I am only commenting on what I know from my day to day workings with VMware and every other OS.
However from working with VMware and Microsoft solutions every day of the week, I can say to you that as far as the Microsoft operating system is concerned, every installation / instance of the operating system needs its own license.
This means that If you have physical server running Windows, then it will need a license. Any applications running on that OS installation will then need their own licenses too. Now, when you install a virtual platform on this Windows OS, the application in question is going to have a license and a license agreement according to the vendor of that software.
When you use that virtual software to create virtual machines for intent of running Microsoft operating systems, then each virtual machine is a unique machine / instance, so that operating system that is going to be installed in the virtual machine will need to adhere to the licensing agreements of that OS just like on any other physical machine.
Basically, if you have Windows XP license key, then you are only entitled to have one XP installation and that key would be used for that. Technically you can install multiple virtual machines with Windows XP and then use the same license key in each virtual machine, but then you would be breeching the licensing agreements of the Windows OS. This is how it is outside of OEM.
OEM licenses are the same except they have a few extra clauses. One such clause, is that OEM software is sold and licensed from OS vendor to the hardware vendor. The end-user would then be licensed to that hardware vendor as per the OEM license agreements. Most OEM installations of Windows for example,would contain a OEM license stamp or text file, etc.... which would prevent the software from being moved to other hardware. In other words, if you have bought hardware with OEM WIndows on it from someone like HP, then you will not be able to simply just move this software to another hardware platform like IBM.
If MIcrosoft did not have these licensing agreements, then everyone would be using their software for free ; - )
When installing your next installation of a Windows operating system, you should have a good read of the licensing agreement before you proceed. Most people dont read it when installing, but it does help explain things a bit more.