You do not think they actually look very similar in terms of appearance? I always though ace and luffy did look like they were brothers in terms of appearance, hell both of them even kinda look like roger... Even though ace and luffy most definitely not brothers, they could still be related in some other way(cousins maybe lol)

, well, if you know the true, you begin to find/search the points of difference
I even find Ace more like Dragon than Roger
the same for luffy (more like Roger than Dragon)
cuz of the face and more important : the smile
I know it sound crazy but anyway
And definitely they are related.
