#10 on the "Top 10 Ways to Guarantee Your Best People Will Quit"

Found here:

10. Treat everyone equally. This may sound good, but your employees are not equal. Some are worth more because they produce more results. The key is not to treat them equally, it is to treat them all fairly.

Fairness seems to be make sense. Of course, the law seems more likely to mandate "equal" treatment than "fair" treatment among a group of somewhat similar employees.