How does a circle sit work?

I have done a group/circle sit a few times with varying number of people, and have seen it work (seeing is believing).

Can someone please explain in simple physics terms (Physics 101 for the loss) how this is possible, because I personally felt very little weight on my legs. I think that the weight would be averaged out but even so I thought I would have felt more pressure than that.

http://www.youtube.com/watch?v=8QSwMlCrArE

Thanks.