For example if the skilled one solves the hard problems the less skilled one cannot solve. And if the lazy one spends a bunch of time on facebook.
It isn't about the salary in absolute terms. It's about recognition and to be appreciated for the good work he's doing. But instead he gets the lesson that it doesn't matter.
Now there are two options:
1. Get a new job
2. Stop working so hard and stop caring about the work you do
Both are very bad options for the employer. This can only work if everyone are of similar skill and motivation.