I agree that the temp won't hurt the bikes--some of mine have lived in an unheated shed year-round for 15 years, with temps ranging from 110+ to minus 10. You can create all kinds of hypothetical arguments about moisture condensing in the tubes, plastic and rubber becoming brittle in the cold (not a problem at our typical winter temps of 15-40 F) etc., but as a practical matter it's just not a consideration. If you have one bike you ride most of the winter, though, it's nice to have that one in the basement. It's more pleasant to ride it AND to work on it.
FWIW, we did have a real cold snap a few years ago, or what passes for one here--it got down to minus 17 F and stayed in that range for a few days. The properties of some materials really did change. A guy a ride with said one of his road bike tires exploded when he inflated it from flat to about 75 psi. The rubber just broke up into little shards held together by the fabric.