The original assumption was that the best place to apply RFID in the supply chain was at Wal-Mart distribution centers. But based on experience, Wal-Mart has determined that the distribution centers are already pretty efficient and that the real value to be derived from an RFID investment won't come until it pushes the technology out to the store level. In essence, this is a classic case of a technology being applied to a business process without the analysis required to determine where that technology might best improve the business overall.
Source: Baseline, http://www.baselinemag.com