Steep price to pay for a player whose best years may be behind him. Sure, it makes Washington better short term, but it's Houston that made the smart trade. Houston is getting two quality draft picks that will be both young and cheap. This is how you build a team.
Dallas, on the other hand, would have signed him to a lengthy expensive extension, watched the decline in play, and eaten the dead money.
Smart, confident managements are never afraid to move on. Dallas is getting schooled by their in-state rival.
Probably a win/win trade though.