Even with the disparity between the Finals haves and have-nots, the NBA is comparable to other professional leagues based on the percentage of teams that have played in its championship game/series.
Out of 30 NBA teams, eight have now never appeared in the NBA Finals (Grizzlies, Nuggets, Cavaliers, Raptors, Timberwolves, Clippers, Hornets and Bobcats). Compare that with the NFL, where six of 32 teams have never played in the Super Bowl, and Major League Baseball, where five of 30 teams have never played in the World Series.
One last pair of tidbits about this year's Finals. If the Heat win, both the NCAA men's basketball and NBA champions will be from the same state. The last time that happened was in 1972, when the Lakers and UCLA both won.
If the Mavericks win, the NBA and NCAA football champions will be from the same state. The last time that happened was 1983, when Penn State was the reigning national champs and the 76ers won the NBA crown.