Why doesn't chocolate go bad?
Simple: it has no water. 

Chocolate is a suspension of cocoa solids and sugar in cocoa butter. It is made from fat and carbohydrates only. Bacteria, as everything else, need water to live. They can't survive in something hygroscopic (like jam or honey) or something with no water at all (flour, chocolate, pure fat). Similar for molds. So, independent of temperature, chocolate won't go bad in the sense that it will never grow colonies of bacteria. 

As Hobodave mentioned, it can "grow bad" in another sense. If held at high temperatures (somewhat above 30°C), the chocolate butter will separate from the mix and form a dull yellow-grayish crust on the chocolate surface. Also, if you leave it in contact with oxygen for long enough (many months), the cocoa fat will go rancid. In both cases, it is perfectly safe to eat the chocolate without risking food poisoning. However, the taste is much worse than in normal chocolate.