Well, maybe you should tell that to the kid because he calls my brother "Grampa." I guess I never had a grandfather either since the only grandfather I ever knew was my widowed grandmother's second husband. They were married before I was born, as well. You can KMA because that great man WAS my grandfather, regardless of your "holier-than-thou" definition.
Sorry if your feelings are hurt. Certainly there are situations like you describe where the children involved set the type of relationship and that can help provide a family framework for the kid(s). If you can't see the problem of having the mother's new boyfriend being given some honorific title just because he married her and when there is, in fact, a real Dad involved actively with his children, then you can KMA.
I'm talking about situations where folks artificially and, usually, selfishly, try to re-arrange people to suit themselves.