Short story shorter:
The Bioshock 2 DLC that came out was only several KBs. Turns out all that did was unlock content already on the disc. This is what 2K had to say about it:
"The way our engine and game structure works is that people need to have the exact same content for people to play together. 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."









