I pretty sure what they were trying to get at was that the game is different. If anyone here has a familiarity with Luigi in side scrollers (aside from the original Super Mario Bros), they would see that the jumping mechanics for Luigi are different. As long as the game has new levels specific to the dlc/retail product, then it can be justified.
I believe you are referring to Ensemble Studios with Halo Wars, who were also responsible for the Age of Empire series if I am not mistaken. I'd watch the tongue.
MajorPain10's comments