I think the higher numbers are probably also from places with high COL.
As I said earlier, we are well into double digits (roughly 1/3), and that's for a 1900sqft townhouse that is surely nothing fancy (no granite! no stainless! Oh, the humanity!). In SoCal, that's still a half a million dollar property. So of course it makes up more of our net worth than someone who owns in a cheap housing market.
There are places where a nicer home, fully paid off, is only $100,000. Ours, only 2/5 paid, still accounts for double that. So of course the average person in Nebraska has less of his net worth tied up in his home than they average person in Manhattan.