No reason to swap unproven prospects when the one you already have fits the style of play you are trying to build.
Dallas wants to be hard to play against. At least that was the original excuse of the Avery signing. The GM's admitted they couldn't out-skill Detroit, so they wanted to make it hard to play against Dallas, mix of Anaheim with more discipline (Yes, I get the irony of the Avery signing).
Obviously, that has happened this year, but Neal is that type of player. They won't trade him unless they are bailing on their design of the team. Plus, the toughest part of Dallas’ team is injured, but Ott and Lundqvist are getting healthy. So is the newly acquired Sutherby.
The most recent trade, to me, means the Stars are still trying to become a tougher team. They have that in Neal.