This is not like going to a concert... this is a TEAM sport, meaning there are multiple players on a team, they are there to step in when a player is out (w/e the reason)... when you buy tickets to see a band/singer there are no guys waiting in the wings to step in for them!
You, as fans/businessmen of basketball KNOW going into every game there is a chance that you may not get to see your favorite players AHEAD of time! There are no guarantees (said or unsaid) on who you will see at a basketball game, that's why the team is named San Antonio Spurs and not Duncan, Manu, and Parker. If the fans are upset then that's on them for not knowing what sport they are watching!
If I go to see Usher in concert I am guaranteed to see him on stage, if I go to a Spurs game, I am guaranteed to see the Spurs play, not individual players... if I don't see Usher, I get a refund, if I don't see the SPURS play (if it's their fault), I get a refund. Duncan and Parker are NOT the Spurs, they are just players (who can change at any time) on the Spurs team!