Just because nothing happened yet doesn't mean it can't. Before I knew much about proper exotics husbandry and equipment (this was over six years ago) I had a burrowing frog in a tank with a heat pad and no thermostat. She lived in it for almost a year before it went haywire one day and ran over 100 degrees. She's fine now but had various health problems for over a year after that. I wish that one of the sources I had looked to had told me I needed a thermostat.
Just last week my parents, who had much the same view on thermostats as you, called asking why one of their snakes was coiled in the water bowl for two days. I told them it was probably the heat pad, and when they checked they told me a section of the heat pad was reading about 120. Luckily this snake was smart enough to get in its water dish so there were no burns.
I'm a member on about five forums for completely different species and the one piece of advice you'll get on every one of them is that you shouldn't use a heat pad w/o a thermostat.
