@fresco,
Hades
Sheol
Gehenna
Each is often translated as 'hell', yet their meanings are all different.
Were you to tell a 17th century Englishman to go to hell, he would likely retreat to his root cellar for some provisions.
The Jews' understanding of hell (sheol) to mean mankind's grave is in keeping with the ancient Hebrew's understanding of death as a state of inactivity.
The Wikipedia article you referenced refers to some who consider themselves 'annihilationists', an interesting term which I have not considered as yet, but which seems to indicate an understanding of the mortality of the soul.
Think about it: If eternal punishment was a consequence for Adam and Eve, would it not have been appropriate for God to have warned them?