"The Man That Helped Create You"

How do you explain to a 3 year old that there's 2 meanings for "daddy".  Daddy to most means the guy that created a child AND he is there in the child's life as a parent.  However, the reality today is that there can be a daddy that created a child but that's it....it ends there, he is not in the child's life. Normally in such cases it is because the daddy is a deadbeat, a loser with issues and he can't or won't care for his flesh and blood when he should bedoing so.  I imagine the child of such a father will someday be hurt by this knowledge.  I struggle with how I will make my daughter understand that her "daddy" is not in her life simply because that is the rules of the game her mommy chose.  It is not because her daddy is an a$$&*$le that couldn't man up.  Daddy is a wonderful guy...so how do I make her understand why he isn't there for her?  

One idea I tossed around is explaining that this man was chosen by god to help create babies so that they can be with their mommies, the ones they are supposed to be with.    And it would be unfair for this man to choose which of these several wonderful babies to live with so that everyone involved agreed he can't live with anyone because it would hurt everyone elses feelings.  I will tell her that if her "daddy" met her, he would surely be unable to resist loving her and being in her life....but that it "isn't allowed".  But then that doesn't sound quite right and I imagine her longing and fantasy to win him over.  There is no perfect way to handle this, but I hope and pray that I give her the self esteem to overcome this knowledge, and I pray that I am amongst friends that will raise their kids to treat kids that have "different" familes with kindness.  So far I have encountered nothing but support from family and friends and I hope my daughter will feel that same normalcy her entire life.  She may fanticise all about her father, but I intend to surround ourselves with those who will make it OK.