I personally have never winterised a boat in SAC... then again I use it year round and drain the motor after every trip....
I guess you didn't live in Sacamento or own a boat in the winter of '91. I didn't winterize either. I lost a engine along with almost every other boater in the Sacramento valley. Mother nature will throw a surpise everyonce in a while. But, since you drain after every trip you should be ok.