"Wet roads are as slick as ice"

"From 32-39 riding in the rain is a hypothermia ..."

Wet roads provide about 90% of the traction of dry roads (according to motorcycle research). So, unless your commute like ride the Tour, you are fine. Just watch out for ground that has a funny shine or looks a different color (oil or gas).

The only risk of hypothermia while riding in the rain is if either you crash and cannot get help (I carry a space blanket for emergencies) or if you commute very, very slowly wearing thin cotton clothing for some reason. But, with decent clothing and rain gear you will be more than warm enough 5-19 minutes into the ride.

I commute year around and only say no when ice is highly likely, plus it does rain a bit here in the Seattle area.