If the Caps want to sign Wilson longer-term at this point, they would want to sign him for 5 years at least, to tie up the first couple of his UFA years. More and more, teams want to avoid contracts that end in a player's age 27 year, at least for players that the team feels are its most valuable -- and the Caps see Wilson as a very valuable asset. If he doesn't sign a long-term contract, he'll probably just sign a contract for a year or two, so that he is still in RFA status when it ends.
The players that a team feels less attached to are the ones that they will go year to year on until age 27 (and beyond.)
DSP's situation is totally money -- more specifically, totally arbitration. The rest got a qualifying letter because the players either don't have the threat of arbitration to create a BINDING high salary, the player's contributions to date aren't enough to create a situation where an arbiter would give a problematically high award, or in Wilson's case, the team is already willing to commit to the higher compensation that is coming. But DSP might get a high award that the team couldn't handle within its cap limits without jettisoning someone else they want, and once an arbitration award is set the team CAN'T back away from it. It becomes part of the salary cap computations, period.
