Ok here's a chemistry lesson from your friendly local chemist.
Lithium-Ion cells are not at all like NiCas or NiMh cells. They contain a pressurised solvent based lithium liquid which is highly flammable. Inside the cell, a barrier prevents the pos and neg ends of the battery from contacting.
During the manufacturing process, small metallic particles remain in the solution and when the battery warms, they move around within the solution. This can cause them to damage the barrier and cause a short circuit. This overheats the cell, increases the pressure and the result is a leak or small explosion.
Manufacturing process have improved since all those laptop and cellphone batteries were catching fire and recalled, the risks are smaller but still there. In the rare event of an incident, flammable materials would need to be close by in order for the situation to escalate. Many cells contain protection to prevent any incident, and chargers have circuits to improve safety.
The chance of an incident are very small. However I have been through the terrible experience of losing everything I own in a house fire so yes, I am fanatical about fire safety. Most people get away with taking no precautions but a few do not. I do not want anybody to have to go through what I have been through, call that scare tactics and paranoia if you wish. Risk isnt just about the chances of an incident, it is about the resulting damage that very rare incident can cause.
Andy