So you won't give up Howard for a chance at Paul Pierce or Vince Carter?
Key thing here is a CHANCE. They have to waive bird rights of Howard before they may pursue Pierce/Carter... so what happens if they lose Howard and then Pierce/Carter resign? It's risky. Sure they can get a verbal agreement (unofficial of course) but Boozer didn't hesitate to take advantage of a verbal agreement for more money/play where he wanted, whose to say a snake like Vince, or an unpredictable, introverted homer like Pierce would do? We can't know. It's chancy.
Hell, I would. But Mavs really think Howard is something special. He isn't. Every team has a Howard. Hows he different from a Stephen Jackson, a Caron Butler, a Tayshaun Prince, a Nocioni, a Deng, etc etc etc. dime a dozen player, there are almost as many Howards as there are Mike James/Juan Dixon/Bobby Jackson/etc's. (although the former is more effective than the latter)