This may be reading between the lines, or finding hidden messages in the context of what is being said, but maybe signing an extension is for preparing to do a sign and trade.
 

They are talking about putting a no trade clause or trade kicker of some sort in it. I am thinking that if PP signs the contract and really does want to stay in Boston, he will ask for some kind of no trade clause to prevent that.
 

Yeah, it'll show that he doesn't trust Ainge ;D

I think Pierce is really contemplating his decision. We are all optimistic about our future because we have a lot of young and talented players. But there is a chance that they won't pan out, and Pierce will be stuck on a team he doesn't want to be a part of.