I'm not trying to say that the clubs will behave morally or that they can't be ruthless. But the clubs do have to honour their contracts. If the player turns out to be poor, he gets paid in full for the duration of his contract, unless the club can persuade someone else to take him. If the player gets injured then he gets paid.
There is no equivalent of the player going on strike and refusing to play. You can argue that making an unwanted player train alone or play in the reserves is an equivalent, but the player still gets paid. He gets what is in the contract, while when the player strikes the club is denied what is promised them in their contract. The club may be trying to force the player out, but the player has the final say.
Its the nature of football that there is competition for places. There isn't and shouldn't be an obligation to play a particular player if another is playing better, even if he has just signed a new contract. Players know there is competition for places when they sign. But when the player fails to make the grade, the club has to keep paying him, even if the player slacks off and doesn't try hard in training. He has a choice of taking the money or leaving. As to your examples, Robinson, Gomes, Atouba and Corluka lost their places in competition with other players. Is the root of the Dos Santos situation because Levy is being inflexible over the fee or because the player is lazy in training? Zamora was unlucky and perhaps illustrates that the clubs have disproportionate power for young and journeyman players, while the star players have power over the clubs.