Our dishwasher never seems to clean properly the items that sit in the corners of the racks. This looks like an obvious design consequence of using one circular spinning spray arm to clean a square rack. So how would you solve that problem? I can think of three things off the top of my head that might work better: circular racks, four smaller spinning arms and a fixed square array of spray nozzles. They all have their problems, I'm sure, and since I'm not a white goods engineer, I doubt I've even thought through all the consequences. I just wonder whether it's pure economics that means the single spinning arm design is the only one we see.
Mokalus of Borg
PS - I've always been a fan of the industrial dishwasher with free-moving trays.
PPS - But that's a bit impractical for home use.