Christianity is prevalent in America for the same reason that Islam is prevalent in Morocco or Hinduism in India. Americans don't exactly 'choose' Christianity, they are born into a culture where Christianity is already commonplace, so they absorb it and conceive of spirituality and transcendence in its terms.
Because 'God' is a central figure in the Christian myth.
I'd say yes.
I would update myself on Quantum theory. Death is an illusion.
http://www.robertlanzabiocentrism.com/is-death-an-illusion-evidence-suggests-death-isnt-the-end/
http://beforeitsnews.com/paranormal...that-death-is-an-illusion-videos-2491082.html
Consciousness continues after the death of the physical body.