Some people get used to the bitterness and brag that they can drink coffee black without sugar. This tolerance for bitterness doesn't change the fact that the stale dark roast coffee is still bitter. Sugar substitutes are an effective tool in the consumers' bitter management strategies
We can safely extrapolate that this research shows humans are not naturally inclined to drink bitter ashy woody burnt acrid tar-like coffee. We are more likely to prefer sweeter tasting coffees. That's a high-five for 3rd wave cafes!
Specialty Coffee is fresh, being served and consumed within 3 to 14 days from roast date. By contrast, commodity-based coffee will mostly be what we consider as stale. Specialty Coffee bags have ‘birth dates’, whereas commodity-based coffee bags have ‘death dates’. Most specialty roasters are transparent. They openly display the day it was roasted and also reveal the beans used, including the names of the farms.