If the article told the whole story, you;d be right on.
By being a supplier;s largest customer, wal Mart foces suppliers to comply with everything Wal Mart is doing. Suppliers change their shipping schedule, procuremnet etc in order to satisfy their biggest customer.
This comes to the detriment of other customers, but those accounts are smaller, so the suppliers let them go.
Over time, Wal Mart basically controls the suppliers's operations, and then forces the proft margin down down down. Suppliers are hog tied bevcause they changed their operations to fit wal mart;s demands.
They can;t just drop their biggest account - their whole way of doing business has changed.