I think it's an amazing show of respect for Steve Jobs.
That or they don't want all their thunder stolen.
I really doubt it. I think they'd like to let a little time pass before talking about this stuff again. At worst, they might want to remove the obligatory lines from their presentation that target their iOS competition, fearing it might seem a little gauche.
Update: A Samsung spokesperson issued a follow up statement to CNET, confirming speculation that the reveal was postponed out of respect, following the passing of Steve Jobs. "We believe this is not the right time to announce a new product as the world expresses tribute to Steve Jobs's passing," the spokesperson explained.