gzt:

Senecio: Why are some potatoes sold washed, and yet others are sold brushed. Still covered in dirt?

Combination of consumer preference and processor I guess.

It's actually an interesting cost / benefit balance calculation for the grower.

Potatoes are usually grown in good quality soils, so every kilogramme of soil left on the brushed potatoes is a kilogramme of good quality soil 'exported' from the field. On the other hand, washing potatoes requires a significant quantity of potable water. This is usually not so cheap in commercial quantities, and requires treatment after use both to remove the soil so it can be returned to the field and also to make it of suitable quality to be disposed of within environmental rules.

"growing stuff" isn't nearly as straightforward as the supermarket shopper assumes :)