You are completely right.
I make a Wal-Mart only list of things that I want to buy that I know Wal-Mart carries. I leave the store (every time) with at least 20% of the list unfulfilled because they're out of that item....those items could be out for weeks too.
Two years ago for two weeks the motor oil shelf at the local Walmart was empty of both 5W30 & 10W30 motor oil in all brands. This is no excuses for having stocking issues like that. What if a building supply store decided not to stock 2X4's for a few weeks? Customers get mad and walk out. Their sales would suffer. Sam Walton would turn over in his grave over preventable issues like that. There wasn't a motor oil shortage. Regional product shortages hitting all retail stores are understandtable. That isn't the issue causing this though. Corporate Purchasers and those in charge of inventory are nickling and diming the stores to death.
If the Walmart store 5 miles down the road of a product the chances are the Walmarts within a 20 mile radius are also out. I don't even attempt another Walmart if one is out anymore.