But only those who bought MCC before end of December or something will get it for free, that's why they send all of thsoe who have played the game before end of December a code. An optional update would work for everyone but it's not supposed to be for everyone.
Maybe I didn't get what you mean and understood you wrong.
Ohhh, I forgot that ODST was only for people that bought the game early. My mistake... yeah then codes is the only way to do it.