Are Tesla cars less likely to catch on fire? Maybe. There isn't enough data to determine yet.
Are Tesla cars much safer than gas vehicles when they do catch on fire? Yes! This should be the focus.
Well. There's that chance of the average vehicle burning.
There's a breakdown in the PDF "Highway Vehicle Fires (2008-2010)" that points out a lot of the fires in traditional vehicles (about 40%) are started by arson and accidental, non-malfunction sources of ignition. And that there's reason to believe arson is under-reported:
NFIRS no longer collects information on suspicious fires that may have been intentionally set. As a result, intentional fires may be undercounted. Moreover, due to the volume of fires, many automobile fires are not investigated for possible arson.
Only about a quarter of vehicle fires are considered to be definitely malfunction-related.
I want to see Tesla succeed. But I don't think its hype or alarmist to say that they seem to be malfunctioning in this way a lot, catching fire in everyday situations (like driving down the road) that don't seem to ignite many conventional cars. That's probably perfectly natural; new tech always has growing pains.