All parents divide their labor and time with their children in their own way. I don't think that there is a right or wrong way to do this but it seems like every set creates their own system. In our system for baths and bedtime, I bathed Annika and put her to bed just about every night of her life - until Dagny was born. When Dagny came, Doug took over without any discussion with me and now he bathes Annika and puts her to bed while I do the same for Dagny. It's easier for me to do Dagny because of the boobs.
Anyway, I was talking to my mom last week and she mentioned that my sister and her husband bathe Sophie together. Every night. What a guy that Rob is.