Obviously it depends on how obese you are and at what age, but even a very brief search shows that studies actually show a much bigger effect than the one you state.
That's where I got the 9 month number from.
Of course if your one of those people who has to get a crane to lift you out of your house.... yeah, I guess your life expectancy would be greatly reduced :P It's just a little pet peeve of mine how much people worry about weight, considering how little it actually affects their life span, compared to something like living a gay lifestyle ... which studies show reduces your life span by 30+ years, which you never hear a peep about.