If they did end up rotten, the Oxygen-Nitrogen ratio could have been greatly imbalanced (way too much nitrogen, not enough oxygen), basically rendering the environment uninhabitable by larger organisms (e.g. people). Since oxygen would be present in this scenario, rot would proceed, albeit at a rate reduced proportional to the amount of oxygen present. This would allow the bodies to be significantly rotten, yet not skeletal, after several days/weeks/months, creating the scene witnessed.
All in all, this type of death isn't all
that bad everything considered. Oxygen deprivation basically causes you to pass out and die in your sleep from the lack of oxygen reaching the brain, so aside from the panic of being trapped, it would be a painless death.
Edit: A grammatical error was bugging me.
Edited by Xetherius, 16 October 2012 - 07:43 PM.