Response to J.B.'s Blog on the "Indian Mounds of Wisconsin"

When I was reading the article on Indian mounds, I took for granted that Indians built the mounds because they were religious and had ceremonies strictly for the gods. I like that J.B. found that the mounds could be looked at with two views. One being that the Indians had ceremonies to thank God for what they were given. The second view J.B. describes as more karma-istic in that the Indians had ceremonies because they thought they had the power to control the weather. This second view is a very intresting concept that I think should be explored further.
Even in the article, the author sometimes doubts the truly religious aspect of the mounds since they tend to disappear after a time...the author often attributes the disappearance of the mounds relating to the fact that the Indians didn't need them after focus turned to agriculture rather than death ritual ceremonies.
I wonder then what purpose the mounds had for Indians; if they held a strong religious symbolism (connecting the middle world with the upper and lower worlds) would the mounds just have disappeared? Perhaps their "fading-out" points into a different direction, one without heavy religious symbolism...maybe the possibility of mounds serving as a function in society such as good weather for crops.