Why is it that folks get all upset when they find out their house is "under water"? People go out every day, and buy new vehicles, and other things, that immediately are "under water" 1 foot from the dealer's driveway.

Buy a $60K truck, pay sales tax, "money for nothing", title fees, insurance, interest,  etc and the vehicle drops $10K in value the second it is purchase.  

They don't stop making payments on it, and call the dealer to come pick it up, because of this. Yet, a lot of folks have done this with homes and real property. Why? What is the reasoning behind it? You bought the property, agreed to the sale price and now you don't want to pay for it, because a third party says it's not worth what you paid for it.

Doesn't make sense to me.