I've always thought it was a combination.  Some people are just happy or unhappy and it doesn't seem much related to their situation.  I've noticed with myself that I seem to have an inexplicably cheery disposition.  Even when things are going to hell in a handbasket, I find myself having fun of some sort and then have to sort of reign myself in with "okay, this is serious now..."

But one thing that bothers me is people always bring up that money doesn't buy happiness.  Now, I know this to be true, but they usually use it to refute arguments that are saying the opposite -- the lack of money (or the resources to provide for yourself or family) certainly does cause unhappiness or downright misery.

Maybe we can eventually make language a complete impediment to understanding. -Hobbes