Most of the cheap timer-controlled dishwashers I used in apartments just added additional pre-washes and rinses cycle prior to the main wash if the "heavy" or "pot and pans" cycle was selected.  As you say, I doubt they had that much effect on cleaning unless the machine didn't heat the water and all those water changes brought up the temperature for the main wash.

My current Whirlpool just washes a lot longer on "pots and pans" and heats the main wash even if the option isn't selected.  I think it does a better job than the normal cycle (even with the heat option selected.) 

It's hard to judge the past dishwashers I used because in those days (prior to 2010) the detergents still used phosphates.  Even those BOL dishwashers seemed to do OK for me most of the time.

Ironically, the early Pots and Pans cycles on dishwashers (I'm talking late 50s into the mid 60s) were actually shorter than the 'normal' cycle.   The idea was that pots and pans would be more or less prewashed by a pot and pan cycle, removed and any remaining heavy soil would be removed by hand washing.  This is why these early cycles had a short or no dry cycle.   It wasn't until the mid to late 60s that the cycles were extended or added additional washes.  

On the current "modern" dishwasher in service in St-Lib (a Maytag WU404), the pots and pans cycle adds one wash to a normal cycle.  If the 'sani wash' option is selected, the water is heated through the cycle and it does quite a good job.