The fortunes of Wal-Mart are supposed to be a bellwether for the rest of the US economy. So when the retail giant turned in a lame November sales increase forecast of only 0.7%, observers grew concerned. However, other retailers are reporting post-Thanksgiving sales in line with the more optimistic 3 to 4% growth numbers.So what's up with Wal-Mart?An article in Slate suggests that Wal-Mart may have reached the limit of its ability to cut costs and undersell the competition. Minus that, it must compete on quality, customer service and the overall shopping experience -- factors that level the playing field a bit.Some have suggested that a Wal-Mart backlash might be in the works. But I see an even more fundamental problem, as does the Slate article.When I compare my local Wal-Mart with my local...