Wal-Mart Defying Gravity

In HBS Working Knowledge:     Some interesting points on dangers to Wal-Mart's future.   How can these risks be managed? " ...  How much longer will Walmart's business model be sustainable? Will it be endangered by its size, increases in the minimum wage laws, or other business and social trends that have plagued nearly every other large company in history? Is a company this large manageable? Is Walmart defying economic gravity? What do you think? ... "