Apple Inc. edged past Microsoft Corp on Monday, Aug. 20, to become the largest U.S. company ever, in terms of stock-market value, rivaling some of the most powerful companies in U.S. history: General Motors, Microsoft, and IBM.

"It's one of those iconic companies," Richard Sylla, professor of financial history at New York University's Stern School of Business, told the Wall Street Journal. "When I think of these companies, their products were used by all kinds of people and their leaders were considered geniuses."

Apple became the leader in its market value a year ago, but it was still short of Microsoft's record. Apple's stock-market valuation at Monday's close was even greater than Microsoft's closing high of $616.34 billion in December 1999, though the figures are in nominal terms, not in inflation-adjusted terms. Apple is now more than $200 billion ahead of the stock-market valuation of its nearest U.S. rival, Exxon Mobil, which stood at $405.97 billion, according to FactSet. That gap alone, notes the Wall Street Journal, is nearly as large as IBM's market valuation.

On the other hand, Apple still faces the same challenge as Microsoft, General Motors, IBM, and other heavyweight companies: keeping increasing profits and revenues at the same speed as it gains proportions in both sales and bureaucracy. In addition, it also has to keep developing innovative products and maintain its culture in order to keep its position, especially as investors are still reluctant about the new leadership.

"Capitalism is creative destruction, and as we speak, someone is probably plotting a product that will steal Apple's thunder," NYU's Sylla told the WSJ. "Apple will sell a lot of products, but I suspect that their reign as the most valuable company in the world won't last for more than another few years. These products can be imitated and they will be imitated."

While Sylla may be right about Apple's thunder, there is one thing worth noting: Apple is actually not the most valuable company in the world. Though most reports raised Apple on a pedestal, in fact Petrochina is the world's most valuable company.

"Apple's fans regularly trot out the firm's market capitalization, which is the value of a single share multiplied by the number of shares available," explains The Inquirer. "Apple's stock finished at an all-time high of $665.15, resulting in a market capitalization value of $665.15bn, which some fanbois incorrectly claimed made it the most valuable company in the world. In present day trading and thus ignoring inflation, Apple's market capitalization doesn't top the charts, with Petrochina, a company traded in New York, Hong Kong and Shanghai, worth $722bn."