Best-performing employees should indeed receive the right incentives to keep performing like that & to stay with the company.
However, let's not forget that each & every employee, from the bottom to the very top, is part of a team. No employee is able to perform single-handedly.
So some of the incentive given to those high flyers should also take into account how they perform as part of the team, and their immediate team should also benefit from (i.e. be incentivised) supporting 1 of the top dogs.