What are "reserve/future" contracts? Anyone who was signed to an NFL active roster cannot enter free agency until March. Anyone who was on a practice squad though became free agents at the conclusion of the regular season. Therefore, the Browns basically "re-signed" the players they are interested in having another look at during the offseason programs or in training camp next season. In other words, it's really just a formality that has to be done to keep your practice squad in tact.
What I wonder is at a time like this, when your head coach, general manager, and original team president are all fired or gone, who is the person that makes these moves? For example, Gronkowski was likely signed because he was with the team in training camp, but that was under a "previous regime" almost; who makes the pitch for him to be signed?
As for the other two players, Adams spent the final three weeks of the season on the Browns' practice squad, while Richardson was a highly-touted player in the Arena Football League.
Don't just assume that reserve/future players won't have an impact. Last January, that's how the Browns had the likes of LB Craig Robertson and S David Sims in camp. Robertson basically ended up starting every game of the season as a nickel linebacker and can be a valuable commodity in 2013.