From my knowledge, anything over 400K for a mortgage is a jumbo mortgage and is at a higher interest rate. I don't think that the people that would buy this type of place would get a mortgage. I could be wrong.
A lot of very rich people, have a huge income to live on, but it is entirely based upon their assets, such as stocks. So I bet a lot of people would be able to afford the monthly payment, but not invest so much of their assets into the house.