The firm has never faced any significant crisis. Even when Wal-Mart was a small regional chain, it was still successful. Wal-Mart's decision making horizon is typically very short. While it has larger strategic goals, most of Wal-Mart's success is driven by short-term decision making, specifically with respect to merchandising and with respect to purchasing. One of the reasons why Wal-Mart has been able to operate with such a simplified decision-making process is because all decisions have the same base objective - to lower costs. This singularity of purpose almost entirely eliminates goal conflict. If you examine Wal-Mart's situation vs. The rational decision making process, you can see that the company meets most of the criteria that are the assumptions of rational decision making. This means that almost all decisions made at Wal-Mart are purely rational, thus driven by cost reduction and with strong information.

Wal-Mart eschews group decision making. Enculturation is key...

With a company that successful, it would be difficult for a manager to dispute this rationale, so you see a high degree of buy-in with respect to the organizational culture. While it is true that Wal-Mart does not take advantage of the benefits of group decision making, the company feels that the benefits of purely rational decision making are better. Since they have the luxurious advantage of having the means to make purely rational decisions, Wal-Mart can almost entirely avoid group decision making.
Guthrie, James. (2008) What educators can learn from Wal-Mart about data-driven decision-making. Education Research Newsletter. Retrieved March 3, 2009 at http://www.ernweb.com/public/1008.cfm

Troy, Mike. (2004). Wal-Mart Braces for International Growth with Personnel Moves. DSN Retailing Today. Retrieved March 3, 2009 at http://findarticles.com/p/articles/mi_m0FNP/is_3_43/ai_113230632