I thought this same thing until this summer, however, I think something changed this summer. When they signed Wallace to a 3 year deal, it showed me that they were going to make a commitment to go all out right now, and it also told me that with the probability of the cap actually going down over the next couple of years, I do not think they are targetting 2011 to have cap space anymore, and are willing to take on the right long-term contracts right now.
And the thing is, Nocioni is younger, and he is a better player than James Posey. He is a comparable defender, but he is a much more versatile offensive player. He also does not have a history of weight, and possibly work ethic questions, that may, or may not have weighed in on the C's decision on Posey.
So I still think it is unlikely that they trade for Nocioni, mainly because I don't think they need him enough to take on that contract, now that they have Wallace and Baby. However, I would no longer be shocked if it did happen...particularly if there was an injury.