"Sha" or why my son calls me by name?

My son is almost 3 years old now. He is very energetic, slightly bad because he does not listen. But he is not so terrible that I need Super Nanny's help. He is just behaving like any boy his age would.
Being short tempered, I am amazed at how many bad things he does I am able to accept. Yet, there is one thing that bothers me a bit: he does not call me "Mommy".
I know that any child his age and older should call his mother "Mommy". But for some reasons, my son calls me "Sha". "Sha" does not have any meaning at all. It is just his way of saying my name "Michelle". When he was younger it was difficult for him to pronounce the long name "Michelle". And even though he can say it now, he is used to call me "Sha". The only time he calls me "Mommy" is when he wants something from me such as food, or needs my attention.
I blame my husband for the fact that Little Prince calls me "Sha". I made all the effort to call my husband "Daddy" in front of my son, in order for him to take the habit of doing the same. However, my husband still calls me by my name in front of my son. He even stopped calling me by my entire name and uses the nickname "Sha" just like my son. Sometimes, when I get mad about it, I call my husband by name in front of my son. But it seems that there is no change at all. For my Little Prince, my husband is "Daddy" and I am "Sha".
Come to think of it, I used to hate when couples with children called each other "Daddy" and "Mommy". I used to think that they lost their identity as a married couple, as lovers and became some one's father and mother. I did not want to be one of those couples. My parents are the perfect example. My father calls my mother "Mommy" (not that he is a mommy's boy, but just by habit). And my mother does the same. They call each other by name on very rare occasions.
Should I be happy that my husband still calls me by name even though I call him Daddy? Or should I be worried that my son calls me by my name? Will it have any repercussions in the future?
I doubt it because "Sha" is just a nickname. My son knows that I am his mother. In all the 3 years we have been together, he never mistook me for someone else. His classmates at the daycare center, when they see me would call me Mommy and he would remind them that I am his mother not theirs. Therefore, I should not be worried. After all, it is just a name. It does not mean that he undermines me any less. He loves me whether I am "Mommy" or "Sha".