After reading a short entry from Glenn Reynolds about Wal-Mart, I hit the two links and did some reading.
PROFESSOR BAINBRIDGE would like us to think that because the economy is improving, people are shunning Wal-Mart because of the lower priced, and therefore lower quality, goods that are sold there. Consumers choose to pay slightly more for brands with more name recognition.
The second goes down another track and claims that the shopping experience in general just sucks at Wal-Mart:

I can accept that, but Wal-Mart starts to lose the battle when Target clearly goes out of its way to maintain wide aisles, a slightly more upscale selection of merchandise and a store that’s not downright filthy six days out of seven. Maybe Wal-Marts outside of the Southeast are clean and neat, but I’ve yet to see a store stay clean and pleasant for more than six months after its opening. Those of us with the option don’t want to shop at Wal-Mart; not out of opposition to red state values or capitalism. We shop at Target because our feet don’t stick to the floor while walking down the frozen food aisle.

I’d agree with the second one, but I think they are both missing an underlying factor: Wal-Mart employees have no motivation to do a good job, their compensation and benefits suck. CostCo, for example, has better employee retention numbers and better starting salaries, according to this article. Contrast that with some of the reports about Wal-Mart’s wonderful employment record.
If you know you are just an easily replaced cog in the giant machine, why try to do anymore than just what is necessary to get by? Maybe this will encourage Wal-Mart to put employee well-being ahead of stock holders value and corporate profits in the race for the the all-mighty dollar.
Update: My stylesheet still makes quotes look like crap, gotta get that fixed.