Just think about it this way, why would they sell an extended warranty if they didn't make money off of it? They are cash cows. Sure, maybe 5% of people who buy them get a full return but are you willing to invest that much money with those odds? If you are, I'd go to the casino and put it on a hand of blackjack.
Plus, you have to look at the exclusions. Most of the normal wear and tear items won't be covered which is the majority of what you would need to replace. It's no where near worth it in my book, but some people like the peace of mind it provides.