Investing in Wal-Mart (WMT) has always made sense, the retailer using unprecedented scale and management tactics just this side of a mean streak to make the giant beast ever more efficient, as YCharts has noted admiringly. Wal-Mart forced competitors to become more efficient, too.

Even as its growth slowed, Wal-Mart rewarded investors. Its superior cost management meant that net income usually rose a bit faster than revenue. It used huge cash flow to aggressively buyback shares, reducing shares outstanding, so earnings per share rose faster than net income.

And it paid a steeply rising dividend, sharing the wealth.

Some recent news articles, however, raise the question of whether Wal-Mart management has run out of efficiencies to wring from the massive operation. Bloomberg News and the New York Times have used extensive reporting to show that in some notable instances, Wal-Mart store shelves were poorly stocked, costing the company sales, because labor costs had reportedly been held down so drastically by store managers. With too few workers, shelves weren’t getting stocked frequently or well enough, the articles asserted. The coverage was promoted by the discovery of an internal Wal-Mart report discussing the problem.

The articles suggest stupid cost cutting, the kind that makes a business less efficient and less successful, as managers desperately try to meet goals set at headquarters, yielding unintended consequences. Wal-Mart has disputed the assertions. But given the well-reported nature of the articles, investors would be foolish to ignore them.

Wal-Mart has a history of pushing store managers to extract maximum work from employees, including allegations of illegally withholding overtime pay.

There are basically two possible reasons for the problem. One, Wal-Mart truly has run out of smart efficiency-gaining moves to make, having turned the screws as tight as they’ll go. The other, more likely possibility is that further smart efficiencies are available to management but that at some level the company isn’t smart enough to identify and exploit them. If it’s the latter, time and possibly changes in the makeup of management could help Wal-Mart to become more productive in ways that don’t displease customers.

The Wal-Mart response to the Bloomberg article was the opposite of a company engaged in soul-searching and self-critical analysis:

“Our in stock levels are up significantly in the last few years, so the premise of this story, which is based on the comments of a handful of people, is inaccurate and not representative of what is happening in our stores across the country,” Brooke Buchanan, a Wal-Mart spokeswoman, said in an e-mailed statement. “Two-thirds of Americans shop in our stores each month because they know they can find the products they are looking for at low prices.”