This chorus of almost adulatory approval from all sides of British public life is not that hard to explain. After all, Wal-Mart, the vast megastore chain which, in its 40 years of existence, has risen to dominate and revolutionize American shopping, appeals to that most basic of consumer interests: the purse. Wal-Mart is cheap; very cheap. It lives and thrives by undercutting all and any competitors.