This is a somewhat dated 'truism,' and not just because Koch hasn't been Koch since before Ed Koch (no relation) passed away. The company now known as E1 Music gained a reputation in the middle-00s for being the place where a rapper could make quite the haul—$7 per record, according to Jim Jones and Cam'Ron, who banked off of Koch's independent label during that period.
But even at the time, the $7-dollars-per-CD amount was probably inflated. According to E1 president Alan Grunblatt, in a 2007 interview with XXL, the $7 or $8 dollar amount is "before money deducted for promotion and manufacturing costs." That isn't to say that Koch wasn't (and E1 isn't) a good deal for rappers; promotion and marketing is in their control, and if the rappers have their own marketing set up beforehand (as Jones did), they can make considerably more than an artist at a major label. Just not $7 per CD more.