Some feats are slightly different in the Beginner's Box than they are in the full game, and Toughness is one of them. The version from the beginner box gives +3 hit points, the version from the full game gives +3 hit points or a number of hit points equal to your character level (whichever is greater). Since the beginner box only goes up to 5th level, I'd imagine they left that second part out since it doesn't have a huge impact.