I did not know that you were not supposed to wash all fruits and foods prior to dehydrating them. I wash everything before I cook anything. Why wouldn't you want to wash it? You never know what is on it.
I don't dehydrate (or use) anything that's not been washed, unless I grew it myself. If you're buying them at the store, you need to wash to remove pesticide residue as well as any coatings the shipper used to keep them fresher.
I always wash it all too. I put it in the sink with a vinegar/water mixture. everyone is right, you just never know what kind of pesticides were used on them. That being said berries and grapes are more likely to retain chemicals and other bacteria than fruits with thicker peels.
I thought about the store bought and pesticides too but the place I found it did not mention home grown fruits or store bought, it just said to pretty much wash everything. This is where I was confused since I would think if you grew it, you know where it has been.