True. But there are differences, like how Bioshock is a more linear experience and more focus on the action. You don't really have any need to go back and forth the Bioshock floors, even if you can if you want. And with Bioshock 2 they removed that altogether and made it a fully linear experience. Although, the System Shock games are fairly linear too, but they are better at giving the player the illusion that they are not and then offer some puzzles, like the need to use a severed head to get thru a retina locked door.
Well, Bioshock 2 was a quick cash-in and made by a separate developer from the original - so we should leave that aside.

The original Bioshock did have some aspects of free roaming, though - nothing so complete as System Shock 2, naturally, but the environments were clearly designed with the same concepts in mind: hubs leading to specific story elements, with constantly-respawning enemies and paths opening up as your character developed. Though yes, overall it was fairly more linear and directed along scripted events.
However, from what I've been gathering of Bioshock: Infinite it will be more open, and we may see a more complete return to System Shock's style.