The concept of insurance in blackjack was one of casino's greatest marketing ploys. Many players feel lucky that they can insure a good hand, thus avoiding a loss if the dealer has a blackjack. Like life or car insurance, companies would not offer it if there was not a profit to be made. The same applies for blackjack. The casino offers insurance because it has a huge edge over the player. Not counting the dealer's ace which becomes less relevant in a multiple deck game, there is a ratio of 4 tens to every 9 non-tens. As a result, you have approximately 4 chances in 13 of collecting on your bet. If you had 4 chances in 12, you would be looking at an even bet.
Even Money is another term used when you take insurance whenever the player has blackjack. The player is paid 1 times their bet instead of 1.5 times (for a regular BJ). Most casinos will pay the player right away without actually placing the insurance bet.