Electricians don't really deal with the inside of devices, we just install them and run power and controls to them. An electronics tech is who could answer the question. But what I have been told is that the solid state parts in some t-stats can short out, basically bypassing all power regulation. Some of the higher end proportional t-stats include a mechanical relay (they call them safety relays) that can drop the power out when it is getting too hot, or w/e situation they deem to indicate a problem. I do know most devices in general favor solid state parts over mechanical because they are smaller and cheaper generally, so with my limited knowledge, I think it would more depend on the situation on why it failed, more than the type of thermostat.
short answer to your question though: I donno