Oil is there because the internal temperature of the bean got too hot during roasting. But you can believe whatever of Starbucks' propaganda you want.
As far as the business thing goes.
Explain Microsoft.
Yeah, I believe that's true and usually stop my roast right as the oiliness begins.
But my target for roasting perfection is Peet's French Roast - it's the best bean I've ever had. Now, I haven't bought it from them in 3-4 years, but at least it used to be dark and pretty oily but definitely not burned and made the perfect cup of black coffee.
I still don't know exactly how they do/did that without it ending up as Charbucks.
Trivia: did you know Peet split off from the Charbucks gang back in the early days, when Charbucks was growing beyond a handful of stores? He hated their mass-roasting methods to keep up with the need to grow with cheap ingredients, and formed Peet's coffee, staying in the Bay Area until fairly recently and resisting the Charbucks decline in quality due to mass expansion.
"Oil is there because the internal temperature of the bean got too hot during roasting."
The amount of oil on the bean is determined by whether you want a light roast, medium, dark roast. The darker, the more oil on bean exterior. It is a matter of personal taste and preference. A dark roast without oil is a stale bean -supermarket kiosks mostly contain stale beans. (Safeway coffee, for example, is not really coffee beans .It is made from soybean and Mexican jumping beans. Only a coffee snob could tell the difference, though)