Game Informer's Joe Juba has answered several fan-submitted questions about BioShock 2, based on what he learned during his recent visit to 2K Marin.
Will there be machines that will allow the player to upgrade the weapons that they are using, like in BioShock 1?
I can't confirm this specifically since I didn't see any of them during the demo. However, usually sequels expand on successful elements of the original rather than taking them out. I'd be very surprised if there aren't weapon upgrades.