I'm not sure we are talking all about the same thing.
My Miele dishwasher is a design from 2008. I do not have the newer/newest feature ("turbo") which basically means "I'm not as interested in saving water/energy as in saving time". Nor do I have the newest "save all water/energy you can but run for 4 hours". But I believe the pumps, electronics and programing is vastly the same, just a few tweaks.
In any case, in my machine, the majority of programs are *very* temperature dependent. I can tell that because it's easy to check how long the program took (it's the default time for the next run until the software adjusts it), and, to make things more "interesting", my kitchen is far enough away from the water heater, which allows for water in the pipes to cool down. So, when people are using hot water, or the weather is warmer etc, you see a variation to the typical cycles I use from one hour and forty five minutes to two hours and ten minutes. Vast majority of the times it's about 1:50.
The previous machine (a Bosch from 1999) used to take a bit less in this house, and almost 20 minutes less in the previous apartment, where the machine was essentially just a few feet from the water heater (utility room in the basement right under the kitchen.)
Cleaning was comparable for the most part. What I find is that the Bosch topped up at some point, say, if you leave a crusty lasagna pan out for 4 days and try to run the pots&pans, it might come out still with some stuff stuck on. It seems to me that the Miele tends to clean those much better, particularly if you select the cheese or starch cycle. Still in about 2 hours.
When I had a GE PotScrubber in the mid 90's (the first model that came up with a sensor wash), sure, if you turned off the heated dry, you'd get dishes ready in 45 minutes. But if you turned on heated dry, it would still take 80 to 90 minutes and it would not get cleaner, because it would take over 30 minutes just drying, not cleaning like the Miele/Bosch, which only take about 10-15 minutes "drying" by condensation.
And sure, the GE *could* clean the lasagna pan if it was there for the meal, but if it had been on the countertop for 4 days, forget about it. The GE was highly detergent dependent, if you had a good detergent with plenty of hot water (my heater was set at 140F in summer, 150F in winter, and screw what people think, we did not have kids, elderly or diabetic/sick people in the home we used hot water). If you got the powdered Palmolive Ultra (concentrated with enzymes and perborate) it was wonderful at cleaning, you could get by with Cascade, Electrasol or All, but if you tried a gel detergent, or a cheap powder, the cleaning power would drop a lot.
My Miele also has a cycle (can't remember now the name, possibly Energy Saver) which is designed to be used with incoming water at the very least 120F, and instead of using the sensors to adjust the cycle, it does a cycle that is very much mimicking the old American dishwashers: pre-wash, I forget if it's one or two intermediate pre-rinses, then a main wash followed by I think 3 rinses. That takes about 45-60 minutes and in my opinion cleans just as well as the GE and others did, which is to say, dishes that were recently used (less than a day) come out clean with some dishes not so well washed -- just like I used to have back then. I've used this cycle if I'm more in a hurry than interested in the whole load being uniformity clean, I can always run the 3-4 dishes that were not perfect in the next cycle, which is usually why I would do that. Otherwise, I tend to choose a cycle I know will clean everything so I do not have to inspect all dishes during unloading.
That all having been said, yes, I do believe that some new machines there take over 2 and half hours to clean. I was under the impression that for the vast majority of them, the normal cycle was the one to blame and cycles which will use more energy and water anyway would take less time, it's just that people have almost a fetish for using the normal cycle even though things are dirtier than that.
This is the first time however, that I hear that people think that older machines cleaned better. They were faster, but almost everyone that I know who got a new machine recently has been more satisfied with the cleaning than they were before.
I will believe Keven's word that his GE is cleaning the same as the Miele because my experience is that water quality makes a big difference, I've had machines that were wonderful and people here hated and I've had machines I hated with a passion and people here love. But my experience has been that the longer cycles with enzyme detergents clean much better than the previous processes.
The other thing I'd like to say is that I do not think older machines were better made. Just looking at the insides of some machines you can tell that some had careful people assembling superior components and some have sharp edges where wire harnesses are passing thru or near, some have materials that wear out more quickly etc.
What we have *seen* however, is that machines whose design only last a few (15 or less) years tend to retire quickly, because you can't find new parts.
I do not believe for a second that GE dishwashers were high quality or built like tanks. The best thing the last GE dw I had had inside was a motor made by Siemens, which was on the quiet side. But previous models did not have that motor if I remember correctly.
So, why are those machines still working 30 years later? Because the basic design has not changed for quite a long time. A machine that was built in 1980s still used essentially the same pump as a machine built in 1997 (or it was interchangeable). So you still can find parts, but now that GE started using a different design, you might have trouble fixing machines.
It's the same thing with water valves, or drain hoses etc, that have been the same, or the material has changed but the sizes are so standard that you can still exchange parts that broke.
Same thing with washers, if the drain hose or water valves break, it might be an easy fix even the the machines are from 1945. If, however, the part is some specialized seal, or tub bellows or door boot, you might be out of luck until we have technology to scan the old part and "print" a new one.
Cheers,
-- Paulo.