I think you've quite hit upon it, adrianh.

To say that "experience" herein reflected that in the real-world would be an oversimplification, for there are many who visit the site who are deserving of much, much higher rank than myself, but for whatever reason have not been able to spend much time here, and thus do not yet have an XP rating that would come close to reflecting their actual experience and assistance to the perl community at large.

By my (perhaps limited) understanding, "experience" or XP herein would, for the most part, seem to be an estimation of the helpfulness of a particular individual in regards to the community as made by the community, revised each time the individual participates in the community. Factors that can affect the increase or decrease of XP are probably best covered in the page describing the Voting/Experience System.