This only happens in the internet marketing niche because let's face it, the big gurus are the ones with the big list and the big influence.
I've done some really small scale launches (not million dollar payday yet) in various other smaller niches in health, dating, sports etc. And most of the top 10 jv leaderboard always ended up with some unknown jv partners.
In the IM arena, the big gurus are the ones who are responsible for most of the sales for the product owners. For example, Mr. A (guru) will make 50 sales while normal JV could get only 1 or 2 sales.
Outside of IM, things are a little different. Almost every JV partner make pretty balanced number of sales (not sure if i described this correctly). For example, Mr. B (my #1 jv partner who won himself an iMac) got around 20 sales for my launch while another of my jv partner (no where close to the top 10 jv leaderboard) made around 10 sales.