Here's the comment I put over there:
Jeremy, in my family, we kids always called our father "Daddy." He was Daddy. We stopped calling our mother Mommy (switching to Mother), but Daddy was always Daddy. We never called him Dad. Not once. We disrespectfully called him "the O.M." (for "the old man") for a while -- though not to his face. My mother always referred to him to us as "your father." It's hard to convey the deep sense in which "Daddy" was just exactly what he was. No matter how mature or immature I was at any given point, it would not have shaken that belief. This was not a matter of sentimental love either. The tone could be quite negative, yet he'd still be Daddy.As I got older, I recognized that it seemed a bit oddly babyish to call him Daddy, but somehow it just wasn't possible to stop, even though it had not been a problem to drop the use of "Mommy." Jeremy raises the theory that there's a matter of regional usage here and that "Daddy" is a Southern thing, so let me add that we were raised in Delaware. My father was from Delaware but my mother was from Michigan, so it's possible that we kids followed the regional usage for each parent's place of origin, but that seems awfully weird. I have no memory of either of them telling us what to call them.
A fine point in my family is that early on my father's mother established that grandkids would call her "Mom." My father's father at that point became "Pop." So the paternal grandparents in my family were always "Mom and Pop," and neither of those words would ever seem to be a normal thing to call parents. Thus, we couldn't get to "Mom" from "Mommy," but needing to throw off the babyish "Mommy," we resorted to the oddly formal "Mother." Somehow, the corresponding "Father" never seemed right. And the way to "Dad" was also obstructed. So for the rest of their lives I called them "Mother and Daddy."
Now both are dead, and when I talk about them, I only say "my mother and my father."