That said, there are still going to be issues with this model:
* Customers give their address to Wal-Mart when they sign up and are assigned locations on their way home from the store. So depending on who signs up and how many, there could be gaps in coverage; the point behind this is to lower prices for items shipped online by removing companies like FedEx from the equation, but we don't know if customers will have to deal with higher prices if outside of the independent coverage area or if they'll only lower the price for items as a smaller general decrease that affects the entire potential coverage zone.
* There's still a chance of package theft by unprofessional drivers. I can picture it being a very short time before methods of theft are passed along various channels (including the internet), much like shoplifting guides.
* People don't really trust random strangers knocking on their doors as much as a FedEx or UPS deliveryman, which could cause concerns among customers.
* As the article in the OP mentions regarding Zipments (a similar concept), some cities require licensing for the drivers (which either get factored into the costs of online items if Wal-Mart pays for them or lowers the amount of drivers due to making all new hires pay for their licenses) and Wal-Mart would need to either pay for insurance for the packages or require the drivers to pay additional insurance costs to carry higher priced deliveries.