Oh my. Okay, some things need to be majorly clarified...
First off, the definition of Main Wash: the portion of the cycle where the main detergent cup is dispensed up until the point of draining to proceed to a rinse. Most older machines usually had quite short main wash times, but that has nothing to do with the Full Cycle Time of the machine from start to finish. The later models of the PowerClean had a 12 minute Main Wash, followed by a purge, then a 30 minute or so Final Rinse, when set to its Normal Cycle. So Mark, you are right that it's not really enough time to fully heat the water, which is why a lot of older machines did numerous prewashes back to back to keep the tap water entering as hot as possible. The Final Rinse is what causes the steam when you open the door at the end, because it's typically the longest portion of the cycle, and also a thermally held cycle on the timer/control board.
@jerrod6 - I'm not entirely sure what you're asking but I'll do my best to answer from what I understand. Firstly, a dishwasher must have a filtering system, or you'll just be stuck with particles of dirt and food stuck in the tops of cups and on dishes themselves. There are two types of dishwasher filters, ones that separate the soil from the water with centrifugal separator plates on the impeller and send it into an accumulator chamber to be sucked out and sent away when the machine drains, and then ones that have a manually removable filter that all of the water must go through to enter the pump inlet, capturing soil before it can ever be sent through the wash arms altogether.
Now, the majority of machines with an accumulator filter (Whirlpool PowerClean and Voyager, some older GE machines, Hobart KitchenAids, etc.) have blades that pulverize any food it catches, and the separator slings that soil through a passage into the chamber, where it becomes stuck by the filter mesh. This chamber only empties directly into the drain port, so that water cannot back flush the soil into the wash water again. The water jets hidden on the bottom of the lower wash arm constantly spray down against that filter to keep things loose, and also to help sweep the soil down when draining. Most of these machines just hold that captured soil until the drain, where it gets sucked straight out, so there isn't any "starting and stopping and adding water" that it's not already doing to progress from prewash to main wash to rinse, etc. Now, in the case of the more recent Voyagers, the Automatic Filter Purges were a way to reduce the amount of water needed overall for the cycle, by using the prewash water AS the main wash water simply by removing the soil it captured. A Main Wash - Rinse - Rinse sequence uses less water than Prewash - Main Wash - Rinse - Rinse, because if there were any filter purges during that main wash, the water it used to refill that tiny amount of water drained out to clear the filter is still much much less than having to completely drain the prewash water and refill completely for the main wash. So, in response to your question, self-cleaning the filter is very much an important part along with spraying the dishes because that dirt has to go somewhere, as it's not very productive for it to be flying around in the tub with the water.
Second, "manual" filters in well designed machines are actually quite the opposite. In machines like the new Whirlpools, and in machines like Bosch and Miele, the removable filters still clean themselves "automatically" because the drain port is positioned right under where the filter cup locks in. In the same way the accumulator chambers work, the filter cup serves the same purpose, catching food particles and keeping them trapped until the drain pump kicks on. In machines like mine, the drain pump activates while the wash pump is still running, so that the turbulence helps dislodge anything stuck to the mesh. It will then fill with the equivalent of about a cup of water, and pulse the pump on a few seconds at a time to additionally clean anything stuck in the filter. So far, I've not needed to clean my "manual" filter one single time because the machine keeps itself in order just by basic operation of the pump assembly, and still only uses around 3 to 4 gallons for a generally dirty load of dishes.
Also, I'm not sure of the reason ANYONE would want to clean a filter just once a month if they thought the food was caught and kept there the entire time waiting for the user to attend to it. That would be the worst smelling machine on the planet. Not to mention the bacteria being thrown all over your dishes because of month old food soils being kept around. The goal of both designs of dishwasher filter are not to leave any food at the end of the cycle. The advantage to the removable design is that it's much easier to take out the filter if something like a bread tie got dropped in the machine, whereas the advantage to the accumulator design is the capability of having a disposal blade, but with the inconvenience of having to break out the tool box should a nail or piece of glass fall past the sump grate.
Last note, now that there is a new contender on the roster, there's a bit of a hybrid to explain. The machine that Bob has is built on a design called MicroClean that has no disposal blade, but also has a non-removable, self maintaining filter. This is achieved by a new system where the filter itself is actually spinning with the impeller, and a series of baffles in the pump chamber actively lift those soils away from the filter and direct them to a containing chamber, much like the accumulator but without need of dedicated wash jets on the lower arm. Instead, it's directly open to the drain port and, as you'd imagine, soil gets disposed of as soon as the drain pump kicks on. It's practically a hybrid design that plays to the strengths of both platforms.
Last last final thought, more of a personal one, but I don't understand the irk some people get about a dishwasher pausing now and then. I don't believe theres a machine that sounds a foghorn every time it changes action, and that's about the only reason starting and stopping would bother me. Much like my old Maytag Voyager and my current Whirlpool WDT920, most good dishwashers only have periodic pauses for a few seconds at a time for sensing purposes, but they're so quiet that it's barely even noticeable. And I mean, who honestly is sitting right next to the machine every waking moment, criticizing every move it makes in the first place?
