What defines cooking wine? What makes cooking wines and cooking sake considered only for cooking? My thoughts would be how cooking sake has more spices added to it but I'm not sure for wine.
At least in germany "cooking wine" is more a reference to a cheap wine that just does not taste good if drunken (or is of a low percieved quality).  For example a cheap lambrusco, which you get if you order a few pizzas at your local pizzaria, is considered "cooking wine" in germany.