The thing that you have to understand here is that re-signing Tuch should be Buffalo's top priority when it comes to the player. Unless he demands a trade, trading him would be counterproductive given the current state of the team for several reasons.
1st - Buffalo needs more vets, and has no room for more prospects.
2nd - Buffalo needs more size, not less. Tuch is one of the few big bodied forwards in their top six and would be extremely difficult for a team like Buffalo to replace via trade and almost impossible to do via free agency.
3rd - Buffalo is not a sought out destination for players. By all accounts, Tuch wants to be in Buffalo. Trading out a guy that wants to be there and bringing in a player from a contender who doesn't want to be there would further undermine dressing room morale.
Buffalo is a small market team and along with a couple of other teams in the league, they are in a unique situation and at a disadvantage. Rules and seemingly obvious strategies that apply to 85 percent of NHL teams do not necessarily apply to the few teams in this situation, and they have to build their teams a bit differently. What seems like common sense GMing to most around the league may not make so much sense when you dig a little deeper and understand the nuances going on behind the scenes.