Sorry for posting anon, but having difficulties logging in right now. Also, full disclosure, I'm a property technician for Target.
There's also a big difference in how Target and Walmart design their stores. There are a few stores Target has that uses direct lighting in, one in the greater metro Detroit area. For the most part though it isn't as feasible with how they have their drop ceilings set up. Walmart uses a more industrial design with a high, exposed girder system and full runs of florescents across the entire building. Target on the other hand uses a drop ceiling with an average height of 14ft and a floor with a high gloss finish to maximize the uses of it's grid pattern lighting solutions. Any type of direct lighting would be difficult to add into the brand image Target has for it's stores.
Thanks for the info, I've noticed the difference in style but didn't give it much thought. Still, it would be nice for them to figure out a way to get the best of both worlds.