Hmm, having dismantled all three of my poppers today, I've found a possibly dangerous mistake/design flaw in my Kitchen Gourmet B32-B popper*. This particular popper has an 0808 date code (presumably Aug 2008)
The motor and small element are wired in parallel, and fed power through the main element, thermal fuse and bimetallic thermostat (i.e. in series with these elements), so that when the thermostat overheats and opens, the fan and both heating elements switch off. This was confirmed by prying the switch open and then closing it with a insulated probe while powered up. Once the switch cools, all three components power up again. The thermostat switch is fast enough that the fan speed doesn't drop a lot, and wasn't that noticeable when roasting (I would probably notice it now that I know to expect it).
Although this probably isn't dangerous when popping corn and doesn't stop the popper popping corn, it could potentially be dangerous if the popper could roast coffee to or beyond the 2nd crack point and then have the fan and heating elements cut out, with runaway heating of the beans in the chamber and a possible fire. Fortunately my particular example cut out at around 400F, before 1st crack.
Both the Sunbeam and the JC Penney poppers have the small heating element and motor wired together in series, with the thermostat controlled main element in parallel with them, so that they stay on if the thermostat cuts the main element out, and the air flow will cool the popper. In all cases the thermal fuse will cut all power if it blows. I haven't worked out if there is a simple fix to the Kitchen Gourmet popper wiring or if the mistake is on the riveted heating element section, which isn't easy to modify.
*(I blew up this popper yesterday when fiddling with it while dismantled and powered up trying to understand the circuit - do not try this at home, but I'm used to working with valve amps and materials deposition equipment with >300VDC on contacts. It blew up because I though I could fix the problem with some judicious rewiring, which I got wrong as the small element and motor were still in parallel, so the motor blew when I put 110VAC across its rectifier diodes)