Another interesting thing to consider here: I wonder how the consensus here differs from people of a divorced household from people with a single parent in the picture or a "traditional family". Coming from a split household (saw my dad on every other weekend) the only person who I ever heard refer to my mother as "mom" was my brother and I. Everyone else, including her mother and father + my dad, constantly referred to her by her first name. So really I kind of came to know my mother more by her name than by "mom", and used the latter more as a term of affection or a title rather than what one would traditionally consider a name.
Interesting thread, though, because it's something that's honestly never even crossed my mind before for any number of reasons.