I find the "true believers" tend to be the only ones (if any) who are promoted from within ...and it's almost always because of the little flourishes they attach to their work
I'd also say the work ethic of both types of workers is often identically-sampled (ie there are "hard workers" among both camps): the "mercenaries" just happen to cut their day off when they're "supposed" to far more often than the "true believers" will