This house actually backs up a theory I have that, as you move to more expensive houses, you tend to get more for your money. I know location is everything, but to use one example, my house might go for close to $1M right now. But, when I look at that $15M compound, I'm seeing a LOT more than 15x the value of my home!
But, once you get up into more extravagant territory like that, the houses do tend to be customized. And that's going to limit their appeal. The few people who can actually afford something like that, would probably just build what they really want, rather than taking on someone else's dream home and trying to alter it to fit their desires. And, there's simply more competition for less expensive homes, as there are more buyers.
It's a moot point though, as it's still way too much property for me, and even if someone gave it to me free and clear, the utilities, property tax, upkeep, etc would kill me.