It really doesn’t have anything to do with 220v vs 120v systems. You can easily boil water with 15 amps at 120 volts. We used to have dishwashers with strong enough heating elements in the US to do this from cold running on 120v. It is a lot more to do with the efficiency standards set by Department of Energy, starting in 1994 and then further restricted in 2013 to maximum 307 KWh/year and 5 gallons of water per cycle. Prior to this, dishwashers in the US worked very differently than they do today. This is also why dishwashers in the US do a terrible job of drying dishes now - not enough energy to power a bigger heating element like they used to have.

On top of that, many current built and sold machines (at least in the US) are in fact more complicated than let on above, even the cheaper units, just not how you’d think. In order to try to squeeze as much performance out of those efficiency standards above, many have a turbidity sensor in the water flow path that checks how “dirty” the water is. If it doesn’t detect much, they will stop the cycle early, which means they “use less energy per year on average” (for the above legislation) and then can use more energy in a cycle “that needs it”. This often has a downside of people that significantly pre-rinse their dishes get really bad results from a dishwasher because the cycles will end so early the detergent hasn’t even fully dissolved yet and will be scattered and stuck to the dishes.

They are correct though that most don’t have temperature sensors in them, because frankly it doesn’t matter - they are either able to get to the needed temperature with the energy they are allowed or they aren’t. The only benefit of letting the machine know would be so it can display an error code to alert the user there is a water temperature problem (but most mfrs don’t want to do that because the average user won’t even bother looking up the error code and will just try to return the product or get a warranty service call, both of which cost the mfr money).