Very normal, especially at that age. As he gets older and more independent and learns how to self-entertain, it will pass. Also, it is not unusual for a child to go through phases of preferring one parent over the other. The fact your husband seems to have little involvement, while you are meeting all of your son's needs, is the reason your son chooses you over your husband. And the whole thing about when your son is sick, and then he turns up the crankiness/whining once you walk in the door? That is very normal too!
If your husband continues to be uninvolved, then quite honesly your son (and any future children) will always turn to you to have their needs met. My husband is a good father but he typically only gets involved when I "assign" him to get involved (such as, "hey, instead of letting your 5 yer old daughter sit in front of the TV, why don't you go outside and play with her? Or take her to the park? Or take her for a bike ride?"). My now 17 year old knows this . . . so she looks to me for support, not her dad, and she has commented on his lack of involvement to me. It is very sad. This is the path your husband is heading down.