Stopping the employee to give his best

It is true that majority of employees are not in a position to negotiate with employers for the contract which they have to sign. This position or we can say bargaining power depends on number of factors which has been already discussed in last forum discussion. But my concern is that doesn't these types of contracts by which company owns the right to all work produced during the term of employment forbid employees to go extra mile and give their best. They knows that what they will get will be very little in front of what the organisation will be getting if they are producing anything out of their own interest. What employees do at job is for the sake of job. But if there is no such clause they can actually think in a different perspective and that will be beneficial for the society as a whole. As discussed in class, when the employees are knowing that what they will get in return is some extra incentive or a pat at the back, why they will indulge in any extra kind of activities. Aren't these kinds of contracts forbidding even whose few individuals who can really think differently.