Yesterday Wal-Mart (NYSE:WMT) turned down an invitation to the White House. Today the company has changed its mind. The invitation sent on January 8 was to attend a series of meetings that Vice President Joe Biden is holding this week as he and other members of the administration begin their broad review of gun violence in America. The review follows the tragic shootings in Newtown but it is really the culmination of public and media outrage over a particularly bad year for shootings with Newtown and the Aurora Colorado shooting this summer. So why did the people at Wal-Mart change ...