If that's true, then I'm totally lost. ALL computers, except custom built ones for sole personal use, have an OEM. Dell, HP, Toshiba, the local computer guy, etc. All of them are OEMs. That would mean that the OEM is the "first user" and he would not be allowed to transfer his own product to someone else in a sale.
As far as the EULA I quoted, here's screen shots of a Win 7 Enterprise retail computer (the one I pulled the EULA from) and a Win 8.1 Pro OEM (the Win 8.1 is horrendous resolution because it was taken using Splashtop...sorry). BOTH have the option to "change product key". If MS prohibits transferring OEM versions, why is there an option to change the product key? Since it's an OEM install you could not possibly use another key unless it was an OEM key. But now the initial OEM key is useless because it can't be transferred and what sense would that make?
I think what your missing is this:
1. The software is tied to the computer, not the human that owns the computer. Yes, he can sell his computer as a private party with no repercussions.
2. As a computer business owner you CAN NOT legally purchase a computer and
not reload Windows using an OEM disk.. this is where refurbishers come into play. You are required to bring the computer to a factory-default state before resale.
As for the "Change Product Key" option. There are only a few select cases in which this is used. From what I have had to deal with it is this:
1. To input a different key if your OEM key has been blacklisted. Some keys get stolen and OEM's usually get a special key or subset of keys that is shipped out on many computers. If someone gets hold of this key and it ends up on the internet and MS finds out.. then it will be blacklisted and will no longer activate. Once you call MS and provide them with the blacklisted key they will eventually issue you a new key.
2. On occasion, some systems will "lose" their activation in which case it may be necessary to re-input the OEM key, not change it, but this is the way to get to that prompt via the GUI.
3. If you run a deployment server or run from images, you may not be prompted for the key during an installation, it will just time out quietly after the 30 days or whatever. Again, the "Change Product Key" is how to resolve that.
4. Businesses that have a VLK (Volume License Key) may find themselves in a situation where they no longer have a VLK and need to purchase and re-license their machines individually.
You can "Change Product Key" from NONE to *Something* - So technically not incorrect verbiage, but yes, the wording could be better for this function.
Windows 8 is a whole other ball of wax. Licensing is stored in the UEFI bios so the motherboard is what licenses Windows 8. If the OEM UEFI bios keys are not there it will not work. As a refurbisher you are still legally required to use the OEM installation media but any Win8 of the correct version will work with the UEFI key.
The reason you are required to use the OEM version is because the OEM disks come with all the "Value Added" software whether that be drivers, antivirus software, etc. You may or not want these things, but as the computer originally comes with these things they are legally required to be there for a few reasons:
1. Vendors paid for their software to be there.
2. Drivers are installed and computer works fully at first boot ("OOBE") which provides a "Great User Experience" and gives Windows a good name, in essence.
3. As the customer that bought the computer, you are legally entitled to have the same software that was sold to you, out of the box.. so this limits MS's exposure to bait-and-switch or other legal battles resulting from providing software that differs from an Out-of-Box computer.