For the real world anekdote, all successful businesses that i worked with seem to be tit-for-tat-ers (i never tried to screw anyone and never got screwed, and i'm pretty sure they do apply tit for tat, or else the defectors would be more common). There could be some sneaky cheaters out there, but mostly due to misplaced beliefs of shareholders that a sociopath CEO will do better than tit-for-tat CEO.