Wal Mart didn't "need" Levi at all. But if it wasn't for the changes Wal Mart forced Levi to make the rest of the retail world would have figured out they don't need Levi either and they would already be a company of the past. Levi was close to bankruptcy when Wal Mart offered them a path out, the fact that Levi has found a way to screw up again isn't Wal Mart's fault.
I don't think it was Wal Mart's fault either. Wal Mart has developed a different way to move merchandise and it doesn't need to pay for 300 plus employees sending out their products from a dispatch center. Once less step in the supply chain should reduce the cost of blue jeans.