I work for a company that's in a partnership with Ahold Delhaize. While we were doing some in-store tests of our software product with them over a year ago, the topic of the robots came up. As they say in the article, the main purpose really is just to scan for spills and obstructions.
That being said, I believe the primary driver is insurance-related. The stores are required (or perhaps given a discount as incentive) by liability insurance providers to regularly check the aisles for fall hazards, and the required sweep frequency is pretty high. In a big enough store you'd probably need to dedicate someone to it full-time--I guess in this case they opted for a googly-eyed robot.
