Banks are handing out mortgages of as much as $10 million to the wealthy in record numbers http://finance.yahoo.com/news/million-dollar-u-housing-loans-040001609.html?l=1
Foreigners use cash, they're parking it in hard assets offshore of their respective native countries. U S citizens use mortgages, future asset appreciation, tax planning and use of capital vs. tying it up come into play.