The first two sections of your question were dealt with in a previous answer Sanchayita http://www.theanswerbank.co.uk/Article.go?id=455, as for why Eminem was nearly banned, his album versions of his songs contain enough profanity to render them unplayable on most mainstream radio stations, hence they are banned in their un-edited versions. 'Bleeped' versions are usually played because of the huge sales and success they have generated.