The choice to be buried or cremated appears to be heavily correlated with one's attitude towards religion. Comparing state-by-state cremation and religious affiliation rates, a pattern emerges that reasonably predicted cremation rates at that time.
Baptists were chosen as they were believed to represent a group with high social reinforcement for religiosity. Assuming states with high Baptist populations would be more traditional/conservative in social structure and traditions, it was expected that burial rates would be less likely to have been supplanted by the growing popularity of cremation. This appears to be the case.
With the growing popularity of cremation, a chart of current data would show increased levels of cremation in states with higher Baptist populations, shifting the trend line to the right.
The interesting question is this: Was it the traditions and rituals of active religious life that reinforced burial, or the cognitive biases in the brains of people drawn to active religious life that also biased towards burial? Perhaps time will tell as cremation grows in popularity and becomes the accepted norm, due to economic factors.
The data used in the chart can be found at these locations:
Cremation rates here
Religious Affiliation Data here
Thinking further about my question above, I've found additional data, from a survey by the National Cremation Association:
Cremation survey here
This survey, from 2005, corroborates the by state information linking religiosity to burial, and adds two more factors correlated to the choice of burial -- income levels, and self-identification as being "Black."
The picture that starts to emerge from these elements is one of the strength of group membership being a leading factor in burial choices. Factors -- economic, psychological, social, etc. -- which put a premium on group membership for well-being make it difficult for members to depart with deceased ones, and consequently, lead them to retain their bodies as both symbols of their commitment and touchstones of positive memories. The archetypal example being the policy of military groups to not leaving anyone behind -- alive or dead.
As acceptance of cremation becomes the dominant form of remains disposal over the next 10 years -- due to cost, land and "green" concerns -- it will be interesting to see what symbols and rituals arise in popularity to replace the practice of burial.