I didn't read through the whole thread, so somebody could have pointed this out, but this could have more to do with Posey than Maggette. They may have basically low balled Maggette, making him a 1-2 year offer that would make him a steal off the bench, but has a 20-30% chance of him agreeing to.
I think they might want Posey to make a decision quickly, before other chips fall into place and Posey becomes the center of attention by being the underrated, unsigned hustle guy from the NBA champs. Extending an offer to other players lets Posey know that hey, we aren't going to wait around forever for you to listen to offers, especially if they believe Posey is willing to stay in Boston for somewhat of a discount. In a nutshell, I think the team recognizes that the longer Posey is unsigned, the higher his price goes..