What Makes an Official Xbox 360 Dvd Game Different Than a Home-burned Copy?

If you burn an ISO of an xbox game it won't play on the 360 without a mod, what's the reason for this? Is it burned into the disc or something or is it just code?

Suggestion:

If I remember correctly, there's a security code, or something of that nature, physically burned onto the Xbox 360 disc (I think it's near the center hole). Without this code the Xbox views the game as a DVD.