Harry never had to drag Cedric, though. Remember that while Harry and V's wands are connnected, they "glided away from the tombstone of Voldemort's father and then came to rest on a patch of ground that was free and clear of graves". At this new postion, the cup is now between Harry and Cedric; Harry has to leap over the cup to reach Cedric's body. (He does this, and then accios the cup.) The fact that Harry had to bypass the cup to get to Cedric always made me feel that fulfilling his promise to Cedric was especially heroic; wouldn't it be tempting to just grab the object you knew was going to save your life, and get the hell out of there?
I mean, it seems to require a lot more fortitude than just flinging yourself onto a corpse and then "accio"ing the cup.