I see delivery robots being significantly easier to create than driverless cars. All you need is a shopping cart stuck on top of a set of stair-capable movement system, it's not like the thing needs to be dressed up as a butler.
Stairs are only a requirement for humans; drones can be far more flexible. Attach hoists to the side of the building, let them in through windows (or cut doors for them). Easier on both parties: no additional stairwell traffic, less chance of the drone tipping over and hitting someone.
Excellent point. Not necessarily practical everywhere, but a much better outside-the-box solution where it works.