I don't know what you're trying to get at with your clean dish equivalency.
I understood dssh to mean that a dry plate is no more suggestive of the plate not being washed than dry lettuce in a salad is suggestive that the lettuce hasn't been washed because both items are supposed to be dry. A wet salad dilutes the dressing. That's why for the home market, salad spinners are popular.
Yes, restaurants wash lettuce and other fruits and vegetables. If you've ever washed your own lettuce, you know there can be dirt and bugs in a head of lettuce (and lots of sand in spinach and bok choy.). So if restaurants weren't washing lettuce, you'd encounter dirt, sand, and flies with frequency. It wouldn't make sense for most restaurants to use pre-washed salad because there's a premium charged for that convenience, restaurants operate on pretty tight margins, use a lot of lettuce for salads, sandwiches, garnishes, etc., and prep cook is a pretty low paying job.
Prep work is typically not done during service, and is normally done where customers can't see it, even at a restaurant with an open kitchen, so that's why you've never seen a restaurant employee washing lettuce. Neither have I as a customer, but I've seen loads of lettuce be washed or done it myself as a food service worker.
