: Not an update really but additional content that didn't fit on the disc. Why
: not two discs?

Since 343 isn't being clear on what multiplayer components are actually available on the base disc (so far, we've gotten "some custom games"), it's a real shame that a significant amount of content for this game will disappear once the Live servers cease to function.

Remember how you could at least tunnel Halo 2's LAN over the internet after the shutdown of Live? Yeah, now if you lose your data, you're just completely SOL on having the mode at all.

The original versions of Halo 1 and 2 and 3 will be preserved for decades. The MCC versions will not.