The Paths of the Dead

I've scanned the forum for a thread on this already, but I didn't find one. If I'm repeating a discussion, sorry.
RotK has many things that bugged me - being a book purist in this case - but one of the things that bugged me most was the Paths of the Dead. The way the movie portrayed it made it seem like the Dead couldn't feel it was time to take care of their unfinished business, which is something I saw in the books. If I remember correctly, in the books the Dead knew it was time to forfill their oath. Perhaps Aragorn yelling; "Let us pass, and then come! I summon you to the Stone of Erech! " had something to do with it. After that, some hours later into in the book, Legolas states that the Dead are following. For those of you whom have read the books, you might remember that Aragorn talked (in general) to Dead at the Stone. And then he stated who he was etc. leading to the Dead following the Company.
So, why did the movie makers use Aragorn's sword instead of his presence as the main reason the Dead knew who Aragorn was and what was going on in the movie? I think it would have had a greater impact had they left out Aragorn having to confront the King of the Dead sword to sword. That was rather pathetic in my opinion. BUT am I missing some point that was made? Did the sword need to be made into some great and feared object of the Dead?