(The following comment agrees with you, it is not intended as an argument against what you’re saying):

Technically being able to contain the content and actually being able to boot the game from the disc (after transferring to the console hard drive) are two separate things. Even without counting Day 1/Day 0 patches. Some games refuse to run without downloading additional content that isn’t on the disc, others require talking to a server even if you’ve just downloaded the latest updates, others. A patch to fix bugs and add content is one thing, refusing to play entirely is another.