I'd think if they did that study on the general population, they'd find that most overweight people had suffered 'mental woes' or depression at some point in their lives, not just those seeking weight loss surgery.
I've never had classic depression symptoms, but I've certainly had some depressing moments because of weight - like when you can't find anything that fits/looks nice in the wardrobe, so you decide you're just too fat, & you don't go to that social event/party. Someone makes a comment, & it has you upset/down for days. I'm sure most of you can relate.
I had my lap-band placed nearly 2 months ago, & have lost 18kg so far. It is something you have to commit to as a lifestyle change, not a 'magic cure'. The band helps with the portion sizes, & feeling full sooner, but the owner has to still choose healthy foods, & exercise (I've been hitting the gym 3x weekly)
Liquid calories - icecream, chocolate etc will go down very easily, so it is quite easy to 'cheat' the band, as some of your friends have done. I choose not to 'cheat', though I want to live like a normal person too, so I am sure that if we're out & I want dessert, I WILL have a little. Right now, I'm enjoying the weightloss, so I've just avoided anything like that. The key, like all weightloss efforts (& slim peoples' meals!) is moderation!