Why would anyone a) pick up the team option, or b) trade for him after that? That's guaranteed money. $11.8 Million. Straight cash, homey.

you think a team can pick up an option on a contract, then trade him and the next team won't have to foot the bill on that 11.8? Sorry but his contract isn't written that way. And he can't be traded before then. Either the Wizards pick up his option, or Josh is a free agent. Josh's best value was being used as an expiring contract this season. Which the Mavericks did.
Dampier's contract, on the other hand, can be traded, and he can be dropped by his new team with no money owed to him.