Before reading too much into Buffett's stake in Exxon Mobil, consider these additional points:
1. It's much better than gold.
In a portion of Buffett's annual letter in 2011 on why gold was not a good investment, he used 16 Exxon Mobils and all of the farmland in the U.S. to make an analogy about assets equal to the then value of the gold market: $9.6 trillion.
"A century from now, the 400 million acres of farmland will have produced staggering amounts of corn, wheat, cotton and other crops—and will continue to produce that valuable bounty, whatever the currency may be. Exxon Mobil will probably have delivered trillions of dollars in dividends to its owners and will also hold assets worth many more trillions (and remember, you get 16 Exxons). The 170,000 tons of gold will be unchanged in size and still incapable of producing anything. You can fondle the cube, but it will not respond."
The irony at the time was that Berkshire had just sold a small stake in Exxon. So maybe it just took Buffett a few years to reconsider his own argument and begin amassing his stake in 16 Exxon Mobils.
2. It's better than cash (and maybe the safest thing the market has).
Berkshire Hathaway's biggest problems may be finding a way to stay ahead of the S&P 500 (which slammed him in 2013) and ultimately replacing Buffett, but finding investments for its cash so the money doesn't sit on the sidelines is also critical to its performance.
While Buffett has been talking elephant gun for a few years, he has yet to deliver on an acquisition to match the Burlington Northern deal. If the cash is burning a hole in his pocket, better to keep it in the market's closest equivalent to cash than cash itself: Exxon Mobil.
In fact, for an example of this strategy in the past, when Buffett acquired Burlington Northern, Alleghany was one of the railroad's biggest shareholders, at 34 percent of the company. The investment holding company suddenly had a ton of cash to invest. Shortly thereafter, Alleghany made a big investment in—yes, you guessed it—Exxon Mobil.
—By Tim Mullaney, special to CNBC.com