Remember that the normal rule doesn't give werewolves resistance; it gives them flat out immunity.
I think this new variant is better because it makes their resilience more evenly applied to weapon users and casters. It also brings real mechanical weight to the thematic importance to silver because magic weapons no longer get the same benefit. If you don't have silver you can't kill the creature. You'll have to just lock them up somewhere. At the same time, you only need one silver hit per round, and everyone can otherwise participate in damaging the creature, whether they are a caster or a weapon-user.
I'm rarely a fan of changes of this sort, but this a really good way of doing it.