I experimented with my VIC-20 in the early eighties, and found out that its RAM retained all data very reliably if I pulled the power plug for less than a quarter of a second. I then used this for debugging.

Later I had a handy friend install a real Reset Button on it, which felt like real luxury.

VIC-20 had static RAM (SRAM) while current memories are almost exclusively Dynamic RAM (DRAM). SRAM stores the information in the way the currents flow inside it, whereas DRAM stores the information into tiny capacitors. The charge in those capacitors discharges with time, so each one is refreshed at regular intervals while the memory is in use. The colder the memory the longer it takes to bleed the charge from it's cells. And that is exploited in these cold attacks. They could put sensitive info into SRAM, because that will lose it's state immediately when the current is interrupted. Of course they would need to put those memories into the devices first, before they could use this method.

Yay for the guys from my alma mater.

Looks like an oversight by the manufacturers. The issue of data remanence could be easily resolved by draining all the energy immediately during shutdown by adding an emitter-follower cascade circuit, much like those used in solid state refrigeration devices.