You are correct. MOST participants in ANY event just show up on Friday night and follow orders all weekend.
From my experience, I medium sized event (100-500) participants, with or without public, takes about 1 1/2 years to plan and execute.
In that time, you work with VERY few people in my experience, to help along. This was done on purpose in my events because I pick the right people who multitask.
At Payne's Farm (was that over two years ago now!), we had a planning committee of THREE. Then we had the following folks help out:
Logistics crew of about 12 men
Wood cutting crew of about 10 men
Webpage designer and updater
Toilet man (not a reenactor)
Water supplier (reenactor who lived around the corner)
I'd say about 25 guys total of the 250 participants. Now, we had folks from Europe show up for the event, so they can't be counted on to help much before on site. For this event, about 10% of the guys could say they helped out putting on the event. Without this dedicated 10%, however, NOTHING gets done.
I would think that the percentage would go down quite a bit with events with larger numbers as it is probably the same small number of folks running things.