I use "Daddy" in my fics mostly because Lois did use it, several times, on the show. (Same with when I have Sam call her "Princess" - it was on the show.)
However, at 31, I can say that I use the term "Daddy" as a term of endearment, though not quite often. My Dad is usually "Dad." But I'll use Daddy sometimes. No real reason for it. I just do it sometimes. Sometimes I'm trying to be super-sweet (about to ask a favor, like can you come help me get my tractor-mower fixed). Sometimes I use it when not even speaking to him directly. (So, Mom, I was wondering what to get Daddy for Father's Day.")
I use Daddy a lot at home now, because of my girls. Although, half of the time it's "Daddy" and half of the time it's "Dada." (After all, my girls are only just going to be 9 months old in a couple of days.)
