I'm really not sure what you are trying to get at.. are you saying that you shouldn't use glass tanks because even though you use a thermostat, the glass still "could" get hot enough to burn your animal and if water happened to spill it would crack the glass?
I'm no scientist or anything, but lets say your glass was 92º and your water bowl filled with room temp water at 80º spills over the glass. Is a 12º temp difference really enough to break the glass?
I spray room temp water on my glass tanks that house my arboreals and my glass is just fine and the glass is kept around 100*. It is also fairly thin though.
I just truly don't understand the point you are trying to make. Almost all newbies start out with unregulated UTHs on glass tanks and I've not seen many, if any at all, come to us with broken glass issues. I'm not denying that it happens, I've seen it with my own eyes.. but that was with something coming out of a 400* oven, not sitting at a common air temperature.