For me at least it is possible to have an orgasm from only anal stimulation. It is harder to achieve and there normally has to have been some great foreplay (which in some way may contradict the above "only anal" statement.... ) but it is still possible. i have experienced light anal orgasms with my very vanilla husband so i know it is possible without adding in the other body parts, extra experiences, etc.
When other parts of the body (depending on the parts) are included it can be more intense. If it is another of my pleasure zones, other then including vaginal, then the orgasm is stronger but still leaves me with the feeling of the "need." Only when vaginal/clitoral stimulation is included in the orgasm does that need finally feel satisfied.