Wish there was more information on the study.... did they take into account that the long sleepers may have had other influences in their lives?
I spent quite a bit of time a few years back with this sort of issue, and I finally figured that it wasn't that I was sleeping too much, but the sleep I was getting wasn't any good. In my case it was specifically Sleep Apnea (though I've not been to a sleep clinic to verify, it's the most likely cause)....
After years of being told I was just lazy... and just about driven to depression because of it... I made some minor changes and learned to live within my limits... and I've been much happier for it ever since.
For me it's helped to sleep on my side (though now my old bed doesn't have the give it needs and I'm waking with lower back pain, and occasionally pain in my hips), but if I get around 7-8 hours a night consitantly (I can do the 6 or less hour thing once in a while, but I can't do it more than a few days in a row)... I'm usually good to go, much better than I was years ago.
Don't be quick to call people lazy, even though I am somewhat, it wasn't the reason for oversleeping.
Interesting article though... there have been those days (years ago) when I've slept in all morning, and then was so tired it was only corrected by going back to bed for a few hours
)