Why do hot rocks burn, and heat pads not (as much)

[Eric Alan]

So it is simply the fact that no t stat, not because anything inherrent about them because they are in the form on a rock?

Pretty much this. Both products are meant to create a heated surface for a reptile to rest on top of. The key difference is that the rock is intended for use inside of the enclosure, making it much more complicated to temperature regulate properly.

Reasons given by lizard people usually are that reptiles don't feel heat on their bellies and don't know it is hot, but snake guys use UTHs. Also something about "hot spots" on the rock. Doesn't really add up.

If you think about how heat transfers in nature, it will help clear things up for how burns happen in captivity. If a reptile lays on a warm surface in nature, their bodies absorb heat while the surface loses it. The surface itself typically doesn't generate it's own heat, so reptiles didn't have a need to develop the nerve endings to be able to sense these temperature changes that seemingly defy nature. In captivity, our heat surfaces don't lose the heat they are transferring to our reptiles. Thus, if the surface is on the hot side, it will continue to be on the hot side regardless of how long the reptile stays put. That's why it is so important to be able to regulate this kind of heat inside of your reptile's enclosure.

In regards to the rock's "hot spots", they are side-effect of the heating element used and the shape of the rock itself around that element. UTHs, whole not perfectly even 100% of the time, do not have the inherent design flaws that add to the temperature inconsistencies.