Gotcha.
I understand your PoV, but I see it from the MS perspective, too.
Look at it, though, as (approx) a £140 product that you can buy for £70 (or whatever),
provided you accept a couple of limitations .... much like non-open air fares. Not prepared to accept the limirations? "That's perfectly okay, Sir .... that'll be £140 please".
It's like buying the cheap, restricted airline ticket, then moaning when the airline won't let you change flight dates. Generally, when flying for leisure, I book a restricted ticket. When flying for business, I make sure it's open, because plans can change, at virtually zero notice.
IIRC, strictly speaking, end users aren't supposed to be buying OEM versions anyway. They certainly weren't, originally, though these days it's more honoured in the breach than observance.
The idea was system-builders sold ready-built systems, OS included, ready installed, and the system builder supplied the support (which, as you said, is the other thing not included in OEM licences).
I guess whether an upgrade is an upgrade or a new machine depends on the extent of the upgrade. If you upgrade case, psu, mobo, processor, ram, gpu and storage subsystem, is it a new machine?
IIRC, MS (and others) get round that one by defining what constitutes an alllowable upgrade, or a non-allowable transfer. And you agree to the licence conditions by using the software.
I understand where you're coming from, but on this point, I see it like MS does. If you want to transfer to another machine, buy the full retail version. I did, and for exactly that reason. If you want the cheaper version, it comes with restrictions, like cheap airline tickets. And those restrictions are
why it's cheaper. You can't have your cake and eat it ... or not without risking ending up with a "non-genuine" bit of cake.