I always viewed the Celtics as more of an ensemble cast.
More like the '04 Pistons than any of the Bulls teams.
Who was the 4th or 5th best player on that Pistons team?
Ben Wallace, Chauncey Billups, Rasheed Wallace, Rip Hamilton, Tayshaun Prince. I think losing anyone of those 5 players would hurt the team and upset the fan base and greatly hurt the teams chances to win (I think it softened the blow that Ben Wallace left for more money, and had never really signed a big contract in his career, and the Bulls/Pistons weren't rivals at the time).
Different from the Bulls where it was:
Jordan, then a notch below him Pippen, and then everybody else below that. Where if the Bulls lost Rodman or Kukoc or Harper or Longley or Kerr, it would be a lot less upsetting and wouldn't hurt the teams chances as much because Jordan and Pippen shouldered so much of the load.
Because the Celtics are viewed by many as a "team" and preached ubuntu, that's why it's so upsetting to lose Ray. If the team was more superstar driven, like Jordan's Bulls or the current Heat, it wouldn't be as big of a deal I think.