Are disenchanters getting robbed by rolls?

Sardonis sent us a note the other day, with an interesting, if probably controversial, point inside: when we're in instances, Skinners take their skins, Miners take their ores, and Herbalists take their herbs (or of course they rotate around if there's more than one). At the end of the instance, we don't sit down and /roll on all of the herbs or ores that people have picked up. So why do we do it