Why is it that DH can play on the computer while I entertain DS but he won't entertain DS while I'm on the phone for five minutes?

Why is it that HE'S tired when I was up with DS in the middle of the night?

Why is it that DS needs Daddy in the room to go to sleep, but Mummy can kiss him goodnight and he'll read a book to sleep? (Haha, I love my son! OK, last night only, but I still love him.)