I think leadership occurs regardless of whether it is explicitly stated or not. If you look at that definition, anyone who enlisted the help of others to achieve something for MM (or, at least, sought approval from others) was a leader. I once had "project leader" as my title instead of newsletter, and I like this term. MM has had many project leaders.
I would even argue that this is the only sort of leadership that MM is capable of facilitating in its current form. The concept of equal ownership to all members doesn't allow a "leader" in the sense of higher influence or authority, as the term is classically applied (or rather how we often envision it).
Of course if you're a leader frequently enough you'll earn a reputation for it. In that sense we have lots of leaders, heavy hitters, regulars, oldies, whatever you want to call it. Unfortunately I think this disparity can actually be hurtful in the long run. Allow me to explain.
At many forums I've been to there is a group of oldies who have good reputation, high respect, or influence. This is usually naturally due to seniority (specifically the "founders"), or high activity but usually early on. It almost always applies to the "golden days" of a forum when it was doing really well, a time that always seems to be regarded more fondly than the forum's present state.
Noticing this pattern at many forums I tried to figure out what it all means. I realized something about these highly esteemed individuals, or rather moreso the way the forum, particularly newcomers, regarded them. There becomes this sense that they've achieved this status and now that they are fulfilling this "role", the position of highly influential member is no longer available. This is either due to a newer member's lack of belief in themselves through inexperience, or the worry it'll be seen as disrespectful or the fear of "stepping on someones toes".
What I'm saying is once forums establish these leaders (again, whether intended or not - this is a natural progression whether observed or stated or completely unacknowledged) newcomers don't feel as though that position is attainable. Because these leaders are of a "higher order" that has already been established, the natural inclination is that this influence is already reserved.
Unfortunately when the leaders aren't replaced and dwindle naturally due to attrition, and as people continue to gaze at the golden days through rose tinted glasses, therby becoming even less impressed with today, the forum in general seems more and more uninspired, and if the pattern continues the forum will fizzle out.
This is what I've witnessed for many of the forums I've went to. But as I post this I wonder if anyone will make sense of this or if you'll all think I'm completely crazy and this is just nonsense.
