I asked this on another thread - Why does the NBA change officails each game? Why not keep the same refs for the entire series and allow the players to get comfortable with the flow? Are they that worried about one ref cheating a team?
there are a few reasons that i have heard
getting to ref in the fianls is a reward for the best in the business (insert joke here). they want to reward these guys on longevity and performance (again, insert joke here).
they do not want one style to dictate the series (one ref calls it tight, favors one team, blah blah blah)
if a ref does not like a coach, or there is friction betweeb kobe and a ref, or KG and a ref, it would not be a long-standing road blokc, just something to put up with for one game, like the regular season.