You don't have to wash the mushrooms from the store - the soil on them is pretty clean but if you get them from cow pies, you could easily pick up e coli.
In general, I would agree. But with the state of food industry and its unsanitary conditions, I would wash store bought vegetables too. Every year there are numerous cases of E. coli outbreaks because spinach, onions, tomatoes, etc were contaminated.You don't have to wash the mushrooms from the store - the soil on them is pretty clean but if you get them from cow pies, you could easily pick up e coli.