Generally, a slip on doesn't require a Power Commander. Will you be able to eek out extra performance gains? Sure. But damage to the motor is a bit overboard. Sounds like someone sold your friend on a PC pretty hard.
Every bike is different to some degree. These bikes come running lean to begin with for environmental law compliance. Adding a less restrictive exhaust will only make it leaner. The problem is that if it's too lean it can damage your motor.