It’s certainly not unheard of for debt to be settled at ten cents on the dollar, so to suggest that such a thing is ludicrous is, well, ludicrous.
Not saying that it’s easy or happens all the time, and I certainly have no idea how often it’s applied to mortgage debt, but it does happen in general.
More importantly, I don’t think every single last underwater homeowner is as eager to walk away from their home you might think.