[disco]

It's so C4/E4 can cover themselves for libel. When the housemates start saying things about people or businesses on the outside, it's impossible for C4 to verify what they are saying, thus they censor it. If they didn't and one of the housemates claimed Tesco's was rubbish, for example, Tesco could sue C4 as they broadcast the libellous comments.

The 'live' coverage is actually elapsed about 20 minutes to allow this editing. The cynical amongst you could argue it also gives the producers the opportunity to edit the coverage to portray the housemates in a certain way.