Beyond that, Burlington Northern generates a healthy amount of cash that Buffett could redeploy into other areas of his business, according to Schoonmaker.

With 2008 revenue of slightly more than $18 billion, Burlington Northern is the biggest player in its industry. In the quarter ended September 30, Burlington Northern posted net income of $488 million on revenue of about $3.6 billion, compared with net income of $695 million and revenue of $4.9 billion in the same period a year ago.

Schoonmaker also noted that Burlington Northern has strong management, another trait that Buffett likes. Though the railroad industry has a number of top-notch CEOs in its ranks, "none of them is better than Matt Rose," who is Burlington Northern's chairman, president, and chief executive. Schoonmaker said "He's an outstanding CEO, in our opinion."

Buffett said he was not interested in buying the rest of BNSF rival Union Pacific Corp., whose shares he also owns. He said he expected the companies to remain rivals for the next half century.

"We won't be making any huge deals for a while," he told CNBC. "I made [BNSF CEO Matt Rose] an offer, he said he would take it to his board, and it took about 15 minutes."

The BNSF deal is, by billions, the biggest ever for Berkshire Hathaway. In 1998, Berkshire Hathaway bought reinsurer General Re for $16.1 billion.

Jack Ablin, chief investment officer at Harris Private Bank in Chicago, said the deal was a bet on the future of coal as a source of energy.

"Because Burlington Northern moves coal around the country, I think Buffett is trying to get into coal but doing it in a cheaper way," he said. "It's leveraged against coal's demand without actually having to buy the commodity itself."

Some analysts said the deal did not necessarily signal a wave of mergers and acquisitions in railroads.

"For an outsider to make an acquisition of a railroad or invest a significant amount in a railroad—you may see more people get interested in that possibility," said George Van Horn, senior analyst with market research firm IBISWorld.

"But as far as seeing railroad themselves merging, I wouldn't expect that right away," he said.

Shares of BNSF rivals rose on news of the deal. Union Pacific gained 8 percent to $59.40, Norfolk Southern Corp. jumped 8 percent to $50.40, and CSX Corp. was up 8 percent to $46.20.

Berkshire said the 50-for-1 split of its Class B shares would make it easier for smaller BNSF shareholders to swap their shares for Berkshire stock. Class B shares were up 2 percent, to $3,343, in premarket trade.

Buffett, one of the world's richest men and one of its most revered investors, is known for making big long-term bets. He wrote in the New York Times in October 2008 that he had been buying American stocks in his personal account—a few weeks after the collapse of Lehman Brothers set off worldwide selling.

"Fears regarding the long-term prosperity of the nation's many sound companies make no sense," Buffett wrote at the time.