I think the fruit salad thing is preprepared fruit salad cos its probably not been washed and cut and has been sitting there for a while. I dont see an issue with buying and cutting up your own fruit salad or the Golden Circle 'in juice/syrup" type ones.
Mushrooms...well I have ALWAYS peeled my mushrooms....its just something I have always done. Feels like its making it cleaner somehow. I dont like how they go slippery when wet (*giggle*) and I dont trust just wiping them...so I peel them.