Here in Vancouver, we receive more than 1000mm of rain annually. My commuter is on the work stand at least couple times a week during the winter, mainly for chain and brake/rim (cleaning) maintenance.

Granted rain can cause premature wear on some parts if not properly maintained, but any justifications (reasons) for not riding in the rain, merely stem from one's dislike for it. Make peace with the rain. It brings forth life and renewal.