I agree with Boring's point of view - after all, the Silm mentioned that Earendil left the chioce to his wife, and she chose to be numbered amongst the Elves even though he preferred the race of his father. Maybe Elros was more like his father & Elrond leaned more towards his mother?
What I still don't get is Arwen would have to make the choice to be 'human' in order to marry Aragorn. After all, she can just marry him and then go West after he died. Seems that she had 2 choices - go into the West *or* marry Aragorn & become human. Why? After all, she didn't have to leave for the west immediately - Celeborn & some other Elves (Legolas comes into mind here) left ME long after that, if I'm not mistaken, and the 'last ship' wasn't the one that took Gandalf, Bilbo, Frodo & Galadriel into the West, was it?