It must be recognized that in its simplicity, the "I'm a fighter" slogan was really succesfull. From a marketing point of view is perfect, it's easy to remember, vaunt the player that defined in this way feel to be really good, it makes perfectly the competitive spirit of a fighting game. And off course Team Ninja has heavily used its advertising and increasing the popularity of it.
I think to not exaggerate if I say that, when the people -especially the non fans of the series- think about doa5, after the graces of the girls in their minds comes immediately this slogan. The attempts to copy it by Namco and Capcom are understandable XD