Maybe I'm more juvenile than the rest of you, but I always assumed Napoleon was trying to foster an erection all of the time because of his well-documented impotence.
"In the 19th century, more complex considerations arose. Another royal penis, this one attached to the Emperor Napoleon, defied the best doctors of his time. This was because its smallness and unwillingness to stand up when required were the results of an endocrinal problem beyond the reach of 19th century medicine. Later in the century Dr Freud revolutionised thinking about sex with his insistence that mental factors were the dominant influence."
Whatever. I don't think this is particularly worth discussing, but that is the interpretation I always had (and I think it might be guaranteed to offend a few people, too).
Marc