Since the effects of Pinning come from the (entirely rational) fear of getting your head blown off, should Resistance (Fear) grant a +10 to resist Pinning?

Narrative logic says yes, but that may make an already useful talent downright indispensable.

Thoughts?

You've more or less answered your own question, there. Logically, yes, it would probably help. As per the RAW, it does not. It's up to you or your GM which you want to go with.