"Don't worry, be happy"
Some "happy" people are simply too stupid and dense to ever realize they've been screwed over, so of course they never engage in revenge. "Don't worry, be happy" works just fine for them. They often go through life as complete doormats and they're too clueless to even realize it.
As to the article's assertion about "negatively reciprocal vindictive types" and "managers find them difficult to motivate (unlike positively-reciprocal sorts, who respond to bonuses or free company drinks by working harder or longer)" that a bunch of bullsh*t - in REALITY there are people who are both excellent workers (self-motivated, highly efficient, not slackers, work WITHOUT having to be told or supervised, don't pad their timecards, AND get along just fine with their co-workers, have plenty of friends, etc), AND who don't put up with any crap. So the whole premise of the study is flawed.
That article seems like typical worthless academic tunnel-vision, considering extremes that don't fit with reality.