Apple—the $700 billion one-trick pony

Boxes of iPhone 6 smartphones sit stacked on a table as customers make a purchase during the sales launch at the Apple Inc. store in Palo Alto, Calif.
David Paul Morris | Bloomberg | Getty Images

Eight years after its debut, the iPhone is still the only thing that drives Apple's stock price.

Despite the launch of the iPad, a TV set-top box and a watch over that time span, the largest company in the world trades off just one figure: smartphone sales for that quarter.

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How else can you explain a stock with a market value above $700 billion and a price-earnings ratio of just 13 times getting hit so hard because only one part of its earnings report fell somewhat short of Wall Street's "whisper" expectation?

There are 33 official products listed on Apple's website, but only one matters. And that may not bode well for the stock if the number of iPhones sold falls for the first time ever in the fourth quarter, as many analysts expect.