Actually, this very thing is what led to my recent post on my path to Arcane Archer. I initially had a very optimal build - 1 Fighter/5ish Wiz/3 EK/3 AA/rest EK, or something thereabouts, I don't quite remember - and statted accordingly. Well, it became apparent pretty quick that the character wasn't a wizard; he's come to strike me as an outdoors type, well-versed in a variety of fields, which has led me to want to take some Ranger levels, and possibly even focus on that class. It's sort of thrown some things for a loop, but I'm just accepting the less-than-optimal-ness of the direction I'm going to go, because it's how the character seems to me.
So in my situation, the build was a starting point that contributed to my sense of the character, but once I actually started playing him, things changed pretty drastically. It's led to some contradictions (for instance, my initial focus on mechanics led to a 7 charisma, which, frankly, I do not roleplay, and I kind of have mixed feelings about at this point), but I've tried to accept and work with those contradictions, since they've come about as a result of my growing sense of the character's identity.
So yes, people do develop characters as you say!