It seems surprising that the best team in the NBA cannot win a road game in the post season, but it is really not a mystery.
A number of years ago, Stern and company made a decision to market individuals rather than teams. Thus we have had the cults of Michael and Shaq, and a few (smaller) others. It is likely that when the rules and their implementation are discussed by NBA officials, that a necessity for promoting star achievement is tacitly acknowledged, especially in the post season.
The post season is officiated a bit differently than the regular season. The coaches who have most realized this and adopted their philosophy accordingly are, I believe, Phil Jackson, Greg Popovich, Larry Brown, and Pat Riley. Detroit is the maverick of the bunch, because they are the team without a superstar, and in many respects they are now suffering the same difficulties as the Celtics. But they have a little more experience in playing uphill. For it is not impossible to win without a superstar; it is simply that the obstacles have to be properly understood and allowed for in the construction of the organization, and the strategy of the team. The Celtics are built to win the regular season, but I'm not sure they are constructed to win the play-offs. In the public eye, do the Cs have a star? They have KG, but he doesn't stand up to Lebron in terms of marketing and popularity. The Celtics have a Team in which everyone has their role, but they do not have one star player who can carry them on his back as Kobe or Lebron can. The player closest to that ability is Pierce, and he has worked all season to subordinate his individual, "go it alone" instincts. This has payed big dividends for the Team, but ironically, there are times in the playoffs when it would have been good to have his unstoppable dominance, the player who hit all the big shots two years ago. This season he hasn't had to.
I remember reading about the difference between bias and pre-judgement. Bias: If I can rule a particular way, I will. Prejudgement: No matter what happens, I will rule a particular way. I suspect that the NBA allows their refs a bit of bias, but not (of course) pre-judgement. This is not a conspiracy theory, simply an observation easily borne out in the playoffs: the home team usually gets the calls, but sometimes a star player can get around this. Of course a team without a spearhead and a style built mostly on defense will suffer under this scenario, because the calls will go against them.
It seems to me that the ideal strategy to take advantage of the NBA bias is one where a team can go back and forth between playing a team game and one where they hand the ball to a star with a strong supporting cast to spearhead the effort. It sounds a bit like the triangle offense, doesn't it? Bottom line: the Celtics have the talent, but I'm not sure that they have the right strategy to win. We shall see.