More interesting that the developer feels the need to let fans know that multiplayer is not just an after-thought.
The fact a different company worked on the multiplayer section makes it obvious this side of the game has been treated respectfully and hasn't just been tacked on. So why the need to stress this further? I suspect, like the majority of us, they fear the multiplayer side of BioShock will be all but ignored by most.
I've no doubt that the game will be popular enough, but I can't imagine multiplayer will compete with the likes of Halo, Call of Duty, or as popular online as the Left4Dead and Borderlands market for that matter. Bioshock didn't need multiplayer, I can't blame the developers for trying, but I suspect it'll take another sequel or two for it's multiplayer to be popular, if it's ever going to be.