Will Your Grandchildren Be Jewish?

I stumbled onto a post (on a non-Orthodox blog) that makes some important observations about the often-heard claim that Orthodox Jews will have (on average) many more Jewish grandchildren than Non-Orthodox Jews. You know what I'm talking about. The chart on the that has been circulating for a few years.

This post asks some very poignant, fact-based questions about this theory and suggests that it isn't true because it does not take into account the high attrition rate in Orthodoxy: link. It seems reasonable to me but I am sure that readers will have further insight into the issues.