As a followup to my last post, take a look at Hollinger’s Estimated Wins Added Stat from this year. Look at the disparity in those numbers. According to this stat the best player in the NBA is worth double the value of the 12th best player, and more than three times the value of the 50th best player. EWA is far from a perfect stat, but it is a great indication of the disparity between great players, superb players, and just very good players.
Now look at the 151st best player according to this stat versus the 301st best player. A relatively minor three "wins" separates those 150 players. The vast majority of the leagues' players have replaceable values - their output is largely predicated by how they are utilized (the system, coaching, chemistry, minutes alloted, etc.) These "replaceable" players have a significant role in your team's success (just compare San Antonio right now with Miami) but on a deeper level are essentially just part of the trickle down effect brought from your top few players. You don't become a fantastic team with a bevy of good but unspectacular players. You become fantastic by having a couple of great ones.