The players who were left off were all left off for various reasons.
Crosby and Iginla were picked as a tandem. Getzlaf and Perry were picked as a tandem. Richards, Toews, and Bergeron were picked to check, kill penalties, and take faceoffs.
Staal and Nash were picked to be the extra wingers on the Crosby and Getzlaf led lines.
Morrow was picked to play on the checking line for a specific role. But Nash ended up there and Morrow up with the Getlaf line.
The most commonly stated "snubs" that people list are Stamkos, St. Louis, and Lecavalier.
But I remember at the time the team was picked, it came down to the following decision:
Heatley, Thornton, and Marleau as a package vs. Stamkos, Lecavalier, and St. Louis as a package.
Yzerman wanted to take 1 complete line with ready-made chemistry. He picked the Sharks trio rather than the Lightning trio.