Doug's right... sort of On average, warranty premiums cost more than warranty claims.
Anytime there's a discussion on extended warranties people post how they've saved money by having one. I believe them. But, they are not a representative sample of those who have bought extended warranties. People are less likely to post "I spent $4k on an extended warranty and have nothing to show for it."
BMW's extended warranties have an inherent advantage, in that they provide the parts and they get a discount on the tech's labor at dealerships.
Insurance is best suited for those losses that would wipe you out: destruction of a house, $1M in medical bills, dying early and leaving dependents, causing a traffic accident that kills 20 people, etc.