I'm sure there are plenty of Mall Warts that it would not be wise to "camp" in the lot of.  And, of course, like any 'good' thing, there are those who will eventually screw it up by pushing it too far, until the lawyers and insurance companies get into it (here in the US anyhow) and cause Wally Mart to put up signs prohibiting over night stays.  Then, we'll get "Wally-Guards" and we'll be required to have a Wally-Permit before entering ...
  Just kidding..Yes, there really ARE RVers who actually prefer to stay over in some Parking Lot..But if you are simply traveling and need a place to stop for some sleep, I have, and still do use Wal Mart as a 'stealth' place for that sometimes.  YMMV..
  Camping?  No, I don't fold out my awnings and put out chairs, fire up the Barbie and kick back in any old local Mall Wart.  But sometimes late at night when I need sleep on the road I feel somewhat less 'alone' in a Wal Mart with half a dozen bigger and richer looking campers nearby..
  Don Hanson