That's basically the case for all american EULA stuff. Not worth the paper its printed on in Europe. Online activation takes the scene of dispute to the us where eulas have legal merit. It's no longer ms wanting to stop some guy in Europe but some guy in Europe waiting for a server in california's OK.
Given previous EU rulings on the transferability of windows licences when someone does take this to court ms is on the line for a fine in the billions.
That kind of court ruling wouldn't affect MS a whole lot, it would just result in some minor tweaking of the license terms.
On the other hand, it would totally upend Apple and Google's mobile app ecosystems.
Also, I'm not really sure which EU rulings on transferability of Windows licenses you're referring to, presumably not consumer versions, since they've never been non-transferably licensed to individuals. Closest thing I can recall is a ruling on Oracle.
Edit: And reading through the ruling/comments, it looks like it might be sufficient for companies to simply modify the TOS to not prohibit sales of accounts, they wouldn't have to put a mechanism in place to allow transfer of licenses between accounts.
Overall I still think the sale of digital goods is silly, it's attempted to apply paradigms of physical objects where they don't apply.