There'll be some bullshit calculus behind the claim, like the fact that technically the king owns Stonehenge, the castles, cathedrals and all the other cool historical stuff people want to see.
Discussion
I think there is at least a little truth to it though. The European continent has a lot of amazing castles but people want to see the changing of the guard at Buckingham Palace. I know I sought it out while I was there.