There is also a lot of technology behind walmart as well. They (use to at least) have the largest private trucking fleet in the U.S. They have the most advanced retail software and the distribution center's are ran very efficiently.

Their logistics is part of the equation to why they can offer things cheaper as well. When hurricane katrina hit, our transportation office sent trucks to New Orleans. We would've been in there the next day with over 20 truck loads of goods for the victims, but the US govt held us up. We literally had trucks sitting and waiting for clearance.

They also give a lot back to communities. I personally got almost $4000 donated to my local herp society from walmart in a three year period.