chautemoc: Explanation:
"The way our engine and game structure works is that people need to have the exact same content for people to play together," 2K Community Manager Elizabeth Tobey writes in the forums. "One of the challenges with post launch content for MP is that it can split the player base, and we want to avoid that whenever possible. For this content, creating the DLC package the way we did allowed for us to not split the player base – so whether you purchase the new content or not, you can still play with your friends."
"I know some of you have strong beliefs about DLC, and I'm not here to sway your opinion or convince you to buy our stuff - if you like what we're offering, I hope you get it and enjoy it. If it's not your speed, enjoy BioShock 2 as we released it."
Tobey does add if you don't like it, they welcome your opinion as "that can be more helpful than people who are really excited, because you help tell [them] what to fix and do better."
Well, it technically IS true. The Unreal Engine (at least, circa UE1) requires everyone to have the same packages. So technically, everyone would have to download the content either way.
Now, that being said, if all the content was ready at launch: It shouldn't be premium.
If all the content wasn't available at launch, you can avoid dividing the player-base by including it in a patch.