Yeah, Silver is easy to get. But...
one could argue, its not so easy to get Silver bullets or Silver-Swords (or Silver crowbars for that matter).
(Murphy made the silver bullets herself, so if none of the PC has an Craft skill or an suitable contact its not so easy anymore.
Shure thats not a problem for NSC's...)
Granted about Murphy, but in actuality silver bullets are hard to make. The same techniques one would use to make homemade normal bullets won't work with a soft metal like silver. Jim didn't do his research there, but it isn't a very common thing to look into, I admit.
Frankly, I think Iron should be a +4 catch, just because so many weapons are made out of it anyhow (an adjustment to the pricing system would be needed, with a +3 availability option indicating that weapons are very commonly made out of the material). Frankly, there's no need to guess if something is a Fae or not...just have your weapons be steel to be safe -- it's negligible effort. Anyhow, it's a bit unclear how much appearance plays into the default catch rules in terms of research.
As for Werewolves, they have kind of the opposite thing going on. Only some of them have catches to Silver and many things that look like them don't (and the Loup-Garou needs very special silver). That muddles the knowledge issue a good bit. Still, normal silver for a werewolf-like creature sounds like a +3 to me...+4 seems a bit too high. I agree with Deadmanwalking's take on the mod, and I'd also say it is ONLY +1 because the catch bonus is so good. A +0 catch that acts like a poison shouldn't get your anything, since it is so hard to get the catch to begin with, imho.