Speaking for myself, I'm a 2-3 cups a day on the weekdays kind of person (up until about 2-3pm at which point I cut myself off). But on weekends I often have none (just too lazy to make a cup), and I've never experienced any associated withdrawal symptoms.
At night, I can have a espresso, coffee, or caffeinated soda at 9pm and be ready to sleep at 11. I've stopped drinking it for weeks at a time before, with no difficulty doing so. All of the stories about caffeine's extreme effects are completely alien to me; I've always considered it a fairly gentle substance.
The half-life of caffeine definitely has a lot of individual variability (3-7 hours is apparently the reference range, but I think the overall observed range is wider with e.g. other drugs or liver dysfunction). I'm not sure whether a longer or shorter half-life would be more conducive to addiction.
A person may have low tolerance/high sensitivity (due to fewer adenosine receptors) but metabolize quickly.
I actually find I have high sensitivity and metabolize slowly, which is why it's important I don't have coffee after mid-afternoon.
My bet is that long half-life/slow metabolism increases predilection for addiction (due to longer duration of exposure), but that's just a guess.