I'm pretty sure this Pope resigned because his views were turning off not only potentially new followers but current ones. His comments on the child abuse scandal in particular were quite disgusting. Given that he is the first Pope to resign in 600 years, I doubt this is about health. Catholicism is very big on taking your duties to your grave.
Kind of interesting that someone can resign from their superhuman role as God's representative on earth. So much for the Divine Right of Kings.
I hope the next Pope is more progressive, or at least capable of smiling once in a while.