Why can I figure out notes in music?

I've been playing bass guitar since I was 13 year old (I'm 24 now) and even though by that age I've learned to read both treble and bass clef, I've never liked reading music for the bass. I've always figured out how to play songs by sound alone. Why do I, and some others, have this ability but others do not and seem almost tone deaf when figuring out the notes to songs?