Guy:
On the other hand; if the above is true, then why is masturbation such a popular pastime?
I think that masturbation is analogous to self spanking. Normally one would prefer sex with someone else to masturbation if that is available, and self spanking is the same; spanking with someone else ( I imagine) is far better than self-administered for the internal reasons mentioned above.
Also there's the issue of being able to stop earlier if you're self-spanking, which immediately changes the experience.
Ona personal note I find that a long spanking implement is necessary for self administered. Haven't tried the bungee cord snapping thing - yet.