Walmart takes strategic sourcing to a global level.  This was inevitable as the company became more global.  One of it’s biggest strengths is its size and as it grows, so too will its advantages:

Mr Castro-Wright has estimated that shifting to direct purchasing could reduce costs by 5-15 per cent across the supply chain within five years – suggesting potential savings of $4bn-$12bn if the retailer were to meet its long-term goal of shifting to sourcing about 80 per cent of purchases directly.

via FT.com / Companies / Retail – Walmart aims to cut supply chain cost.