No Big H, they said that if it was a brand new engine they would look into it but for some reason it won't be happening on my old one. I'd say they know what the issue is but won't let the cat out of the bag therefore it's my opinion that the long service intervals are to blame.
Given the fact that the goodwill came through pretty quickly and no questions were asked (of me at least) about any modifications (which there aren't) they know that they are at fault be it any of the reasons you gave above.
I also confirmed with them whether or not my doing more regular oil changes myself would affect the warranty and I was told that as long as BMW parts (oil filter) and correct oil spec is used and I have receipts to prove this then all will be fine. I don't do big mileage but a yearly oil change will be on the cards whether it's by BMW or by myself/mechanic.