Folklore is a funny thing, it is constantly in flux.
I base my view of how silver effects Vampires, Werewolves, and Ghosts for a large part on the interpretations initiated by Gary Gygax. My personal credentials on this topic are that I am a 1st generation "D&D" Dungeon Master from the 70's.
Subsequently, if you for any reason feel that the VWG-Round is not effective against any certain monster type, please visit the WARRANTY page on this site and read my money back guarantee associated with each and every round that is made available to the public!
MONSTERS : Magical monsters can only be destroyed with magic. So, to kill one, you need to have a magical sword or weapon that was created by a wizard or... is made of silver.
SILVER : In ancient times Silver in most cultures has been regarded as a magical or holy metal. Even the bible outright states that it is a holy metal. Subsequently, in mythology Silver is the one metal with which a "common" mortal can craft a weapon on their own, and actually have a chance to stand against one of these monsters. The Siver is already magical on its own and does not need any hocus pocus spells from a wizard to make it magical. The reason this is true is that the silver exists not only on our "plane of existence" known as the physical world, but it also simultaneously "partially" is physical on the other magical planes. When your silver object strikes the part of the monster here in the physical world, it is also damaging the corporeal part of the monster that is in the other plane. Or, so the mythology theory goes... grin.