While the government's takeover this week of Fannie Mae and Freddie Mac will go down as one of the defining moments of an economically troubled year, a related event signals Wall Street's growing appreciation of Web-based business computing.

Standard & Poor's said it's removing Freddie Mac from its S&P 500 index after the close of trading on Wednesday, and replacing it with Salesforce.com, the 9-year-old company largely responsible for the growing software-as-a-service movement, and in important player in the broader, emerging market of cloud computing.

Salesforce CEO Marc Benioff gave an uncharacteristically humble response to the development when contacted by InformationWeek, implying that Standard & Poor's decision is indicative of a movement bigger than his company. "I am delighted to see cloud computing get this recognition with this decision," Benioff said in an e-mail Wednesday morning.

Earlier this week, the U.S. government took control of Freddie Mac (Federal Home Loan Mortgage) and Fannie Mae (Federal National Mortgage Association), fired their executives, and placed the companies in conservatorship. Freddie Mac's market capitalization had fallen to $614 million by Tuesday, well below the $5 billion required to stay on the S&P 500.

Salesforce, with a market cap of approximately $6.8 billion, will be added to the index after trading closes on Friday.

When evaluating companies for inclusion on the S&P 500, Standard & Poor's considers such things as corporate structure, sector representation, accounting standards and exchange listings, financial viability, and whether the company has adequate liquidity and a reasonable stock price, according to the S&P Web site. At least half of an S&P 500 company's outstanding shares must be publicly owned.

Fastenal, a manufacturer of industrial and construction supplies, will replace Fannie Mae on the S&P 500 after close of trading on Friday.

Among the 10 largest companies on the S&P 500 based on market cap, three are in IT: Microsoft, IBM, and Apple.