Al, of course you can sell the house, and keep the difference. But say a housing bubble bursts, or for some other reason you can't get the house sold, in other words the house isn't worth what it was valued at earlier, then those things come into play.
If the bank is worried that the house is overvalued, then they should require a much larger down payment. No way, should they get a $100 house plus your car, when the loan was only for 85. If they are worried that the house is going to crash in value, then they need to require a larger down payment, 20 or even 30 percent of the house value.
i duno, but I think risking your house is enough heartache... No sane person should risk even more.