No, I don't think Despres is being kept down for the express purpose of keeping his contract demands down. Some teams may do that, and I personally think it can be a smart strategy sometimes, but I don't think it's a concern with this player, and the Pens have shown that they are willing to keep guys up if they deserve to be here, even at the risk of the player playing well and perhaps deserving a higher price tag, or in Olli Maatta's case, having him hit UFA status a year sooner. In short, I don't believe the Pens assemble their line up based on contractual considerations.
I think Despres is in WBS for 2 very simple reasons: in the eyes of the Pens' staff, Despres has not proven to be in a category above the guys who are already on this roster; and as a result of that, he hasn't forced their hand in having to move/waive/demote anyone to make space for him.
This doesn't necessarily mean that they don't like him or that he'll be traded. We simply have no idea of that. It's simply that there has been media speculations or opinions put forward on the subject of him possibly being a guy that the Penguins want to move. This may very well be true, but I don't think the Pens would advertise that to the public because (A) it wouldn't help his trade value, and (B) it would only create a rift & discomfort with Despres and the organization if he were to stay. So I take any rumours as BS until we hear from more reliable sources (McKenize, LeBrun, Dreger, etc.) that Despres is being shopped.
I have only spoken about Despres being moved because I believe there is a VERY strong chance that either Despres or Dumo gets moved; but unlike with Dumo who is still has another year of not having to clear waivers, the Pens are going to have to make a decision soon. There just simply isn't room for all of our top D prospects + Maatta + Letang (to say nothing or Nisky, Martin, etc.) to all play here. It's a simple issue of numbers, as well as team needs and relative strengths vs. weaknesses.