Sleeping more = smoking cigs?

"A six-year study Kripke headed up of more than a million adults ages 30 to 102 showed that people who get only 6 to 7 hours a night have a lower death rate than those who get 8 hours of sleep. The risk from taking sleeping pills 30 times or more a month was not much less than the risk of smoking a pack of cigarettes a day, he says."

I don't know what to think of this study. I've heard this before and wasn't sure about it then either. Is this causal?

""There is really no evidence that the average 8-hour sleeper functions better than the average 6- or 7-hour sleeper," Kripke says, on the basis of his ongoing psychiatric practice with patients along with research, including the large study of a million adults (called the Cancer Prevention Study II). And he suspects that people who sleep less than average make more money and are more successful."

Not that I can cite it... but what about all the research showing declining cognitive abilities with less sleep? I do believe his last statement though - work more = more money = more success (at least thats what I'm hoping for).