Would've been fairly easy to request the ID at the start and refuse to perform the operation if you didn't have a valid one. Heck, that seems the obvious way to do it - less to execute if they fail the ID check.
I think statutory warranty in the UK is generally interpreted as six months of 'fit for purpose.' Since it wasn't advertised as being able to play 360 games I'd imagine it's not covered. Though IANAL.
My question is, how did anyone find out this combination? Is this part of the documentation that anyone can get, or is there a rogue Xbox developer out there sharing this information with 4Chan trolls?