If you're talking about the back room of a walmart store, then maaaaaaybe. But installing static cameras and/or rails that capture EVERY location's contents accurately doesn't scale well with the 1 million sqft standalone warehouses they're talking about. The costs would far exceed any benefit. And gods forbid if you want to reconfigure your racks! Meanwhile, if you can make a $500 drone that can do inventory counts automatically, even if you have to manually program its flight path each time you change your rack layout, you've just saved a crapload of money.

I can think of a few reasons why robots may be more efficient.

  - The Biggie(tm): the time the human spends traveling in racks is wasted time that's paid by the hour. Robots aren't paid by the hour, so even if the robots are half the speed of a human, you can simply deploy five times as many robots, and now you aren't paying people for travel time between pick faces AND you're moving more product with fewer man-hours.
  - Racks don't need to be human-length, allowing more storage in less space.
  - Product is lighter than a person, so moving it consumes less fuel. Fuel costs are a very serious expense in a warehouse.
  - Robots can zip around gathering well-organized product faster than a human can think of where to move next. And even if the robot knows exactly where to take the human, it wouldn't be able to accelerate very fast without additional harnesses/restraints for the human.
  - Easier to segregate high-value product. If the robots are bringing you just the SKU you need then nobody except the facility manager has a reason to be wandering around the iPad locker, which means fewer iPads growing legs. Missing product will be noticed very quickly if there's any kind of auditing.
  - Lower inventory error rate, because a robot will never accidentally pick from the wrong location. Your cycle counts and physical inventories are suddenly looking much cleaner, especially on high-volume products.

With all of that said, "no human jobs are being taken" is complete, utter BS. Where do you think those up-to-40% savings are coming from? Yes, storage space, fuel, rent/property taxes, and shrinkage (depending on your security) are all major expenses, but by far the biggest cost in any warehouse operation is labor. The travel time between locations is time that's no longer going into the pockets of workers.