I remember having a discussion with a lecturer at university once, I think the subject was some aspect of building surveying, the particular topic was freehold land. We were taught (and this's as close as I can remember to his words) 'The freeholder of any land owns the land and 500ft of airspace above it, which is why aircraft aren't allowed below 500ft.'
I then repeated my recently memorised version of rule 5, particularly the part about person, vessel, vehicle or structure and pointed out that I had recently been taught that the 'within' wording meant I could fly within 10ft of the land if it had nothing but grass within 500ft slant of the aircraft. I was subsequently faced with a barrage of 'the CAA is wrong'.
Totally irrelevant to the thread but thought I'd share that little experience...