I loved the original, and I don't care whether a game is multiplatform or not - in fact, most of my favorite console games are multiplatform. There's two reasons I'm not all that hyped about the sequel:
1) It's being made by a different development team. I'm far more interested in whatever project Irrational Games is currently working on than I am in BioShock 2.
2) The best thing about the original was the unique setting and atmosphere. Those qualities won't feel as fresh the second time around.