In a speech to employees released on Tuesday, [Wal-Mart] Chief Executive Officer Lee Scott said the world's biggest retailer needed to take the lead in efforts such as switching to renewable energy sources, and even called on Congress to raise the national minimum wage from the current $5.15 an hour. Some of Wal-Mart's most vocal critics dismissed the efforts as little more than a charm offensive, but others applauded the retailer for taking at least some small steps to change the way it does business.