The posing thing is definitely an issue. But I have had figures crack and leak in standard pose, arms down. The rubber itself is deteriorating, if the arms are bent it just speeds up the process as it is strained and will crack first.
Everyone seems to be also OVER factoring, environmental conditions. I live in a neutral environment, not too hot, not too dry. Figures not exposed to sunlight. They are still rotting though. Oh and add Robocop Ed 209 to that list..
Dx Batman
The Comedian
Alien Kane
Perseus
Mars Attacks figures
Rambo
Aliens rubber bodies
Robocop Ed 209