Teslas are less than a year old and they've made less than 20,000 of these cars in all (wikipedia). Unless somebody can show me gasoline engine cars catch fire at a higher than 1/20,000 rate in their first year of service, this is a serious issue deserving serious attention.
the combustion potential of that bettery is a fraction of what you would find in a typical gasoline fueled vehicle. Sure, there's a possibility of it catching fire, and that is life threatening, but there's the same risk with your typical gas powere vehicle.
The video of the Tesla Model S fire accident is pretty scary. Though it is being justified as being caused by the battery getting damaged by hitting into something and this could be a rare incident, but it is dangerous and could be life threatening. I am sure a detailed investigation would reveal the real reason and something will be done to prevent it, but I guess more research is need in knowing all possible failure modes of of Li-ion battery. Also I learned that the fire from Li-ion batteries is not controlled easily...another area for more research, which I guess is already going on.