Its not that he doesn't have anyone to help him win. Its that he doesn't have another player on that team that can pick up the slack when he is having a bad game. No one else on the Cavs can create their own shot and be consistant. The Cavs are -16 points per game when LeBron is off the floor, the most in the NBA for any player.
The Celtics are just a bad matchup for the Cavs. Jamison cant guard Garnett, Mo cant guard Rondo or Allen, and Parker cant guard anyone. LeBron might have one more in him with the Cavs but who knows. I just hope he doesn't come out and miss a few shots and get down early, then just mope around the rest of the game.