I think that it is pretty normal for kids to test "the limits". Some kids do it more than others, and some parents draw the line a bit more adamantly than others. It's all about getting the desired behavior and attitudes from your kids though.
I think it's testing the limits too. Part of growing up is asserting your authority as a separate person. Some parents never let go and their constant need for control drives their children away. It's a fine line.
Testing limits is one thing but flat out deifying is another and you can quickly spot the difference as they age. I know a few parents who never do anything until the child is a teen and then wonder why they have such a "problem" on their hands.
I think it is natural and it is not only children. Nobody likes to be told to do or not to do something. The trick is inspiring the kids to do what you want them to do, without them feeling ordered around.
