"The team took those percentages and applied the nonlinear dynamics model they created, with parameters adjusted for the merits of membership in a non-religious category. The theory behind this non-affiliation increase boils down to something similar to social networking. Groups with larger numbers and more members offer more attraction to be a part of. The bigger a group, the more members they are able to draw in."
Great way to make it understandable to common people like me :-)
I take it that the main religions are overtaken by the church of Facebook etc.