Investors are used to thinking of the 30 stocks of the Dow Jones Industrial Average (INDEX: ^DJI) from the perspective of blue-chip businesses with solid financials. The returns that these 30 stocks have provided over the long haul have been a linchpin of investing plans for countless investors.

But on Labor Day, it's important to realize that the companies that make up the Dow aren't just profit generators that create shareholder wealth. They also represent some of the biggest employers in the U.S., helping to drive the cycle of income and spending activity that keeps the entire economy afloat.

With that in mind, let's take a look at the biggest employers in the Dow and the impact that their workers have on their respective businesses, with employee counts provided by S&P Capital IQ as of most recently available annual figures:

Wal-Mart (NYSE: WMT), 2.2 million employees
According to most sources, Wal-Mart is the biggest private employer in the world, rivaling the size of the Chinese People's Liberation Army and exceeding the workforces of many other government agencies around the world. Its employee count dwarfs those of just about every other major corporation out there.

Yet over the years, few employers have had more controversy with labor relations than Wal-Mart. A lawsuit dismissed last year alleged that the company discriminates against women, and countless analysts have argued that Wal-Mart's wage structure is insufficient, failing to match up against some of its retail rivals and having a net negative impact on the localities where its big-box stores are.

Nevertheless, it's hard to argue that retail jobs represent the high-quality skilled professions that economists talk about wanting to encourage. Many workers rely on Wal-Mart for their livelihoods, though, and anything that jeopardizes Wal-Mart's workers would have a huge impact on the global economy.

IBM (NYSE: IBM), 441,000 employees
On the other hand, IBM and its tech jobs are exactly the sort of quality high-paying jobs that policymakers get excited about. As IBM has moved beyond the commodity-like business of hardware production to have greater exposure to IT consulting and software development, its job base has moved away from factory jobs toward highly skilled, technically proficient labor.

IBM doesn't have a perfect labor record, having replaced its traditional pensions with 401(k) plans for newer workers a few years ago. But the company has been firing on all cylinders lately, and that's been good news for many communities that otherwise would have struggled to survive with IBM's presence.

McDonald's (NYSE: MCD), 420,000 employees
"Do you want fries with that?" has long been the mark of career failure. But the book Fast Food Nation argued that one in eight workers in the U.S. had at some point worked for the fast-food giant.

As with Wal-Mart, many of the jobs at McDonald's jobs are relatively low-paying. But for young workers, who face one of the highest unemployment rates of any demographic group, even a low-paying job is better than no job at all. And although the McDonald's franchise model removes its corporate office from the front lines, those franchises help many communities provide needed employment where jobs might otherwise disappear.

Hewlett-Packard (NYSE: HPQ), 341,000 employees
Hewlett-Packard is doing its best to emulate IBM's success. Somewhat further back in the process, however, HP is still trying to map a strategy from its big presence in printers and computer production toward higher-margin services.

From a labor standpoint, though, HP is going in the wrong direction. HP's restructuring involves cutting 27,000 jobs by the end of 2014. Some would argue that the jobs that remain should be higher-quality opportunities. But for those who end up laid off, it'll be hard to argue that HP isn't part of the problem rather than the solution.

Keep on working
Collectively, the 30 companies in the Dow employ more than 7 million workers in a variety of occupations. Not all of them are dream jobs for everyone, but without them, the job environment would be a whole lot scarier. That's something to think about as you enjoy your Labor Day holiday.

The Dow's also a great place for investors, but only if you pick the best stocks. Accept my invitation to read The Motley Fool's special report on the Dow and find out about our picks for three promising Dow stocks for long-term investors. The report is absolutely free, so get your copy today.