Know that BioShock 2 DLC we've been promoting this past while? Turns out it's already included on the game disc (or if you bought digital, in the game's data files); the Games for Windows LIVE Marketplace lists the download at a mere 24kb, while Xbox LIVE's does it at 108. If you're really not technologically-minded, the jist of it is there's no way a pack of DLC could be that small in size, so effectively purchasing the DLC is purchasing an unlock code for content you -- in a sense -- already paid for.
It's not that BioShock 2 isn't already worthy of your $50 / $60 (it probably is), it's that gamers tend to feel ripped in paying for content that was obviously left out of the initial release. Unlike Capcom did with its infamous Versus DLC, 2K Games isn't citing "separate production budgets" for the original game and the content (though this could be more or less the case), but is saying it's at least partly due to the structure required:
"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."
To be fair, the game surely had a massive production budget, particularly with the multiplayer and five different studios working on it. When the industry requires such enormous investments, DLC like this is bound to show up. But should you buy it? Seems like a grey area in this case; you'll have to decide for yourself. However, 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."