Many dishwashers only had the water coming from the bottom
In fact, among early dishwashers, they all work that way the impeller machines of course only had a water source coming from the bottom of the machine.
Whirlpool made one arm machines into the 70s, the cool 1962 whirlpool SJU 70 dishwasher only had a lower arm, and it was top rated in consumer reports at the time for its great performance, but as Tom and Glenn says you do have to load them in intelligently, but the machine is plenty powerful enough to get the water all the way to the top of the machine. In fact, if you run one with the door open, it’ll hit the kitchen ceiling.
Tom is completely right in reply 10 probably for consistency alone consumer testing magazines did not bother trying to wash pots and pans and baking dishes, etc. in dishwashers so you really didn’t see the advantages of having a real top wash arm, for the same reason they selldom found the poor performance by the dishwashers that had a center tube only as they just couldn’t cope with a heavily loaded lower rack and wash things in the corners of the upper rack, which is why nobody bothers to build such a design today.
John L