No, that may be true for Wall Street expectations, but it's not true universally. Ford makes one product: an automobile. And by all accounts they are a very successful company.
And as far as that goes, Apple has always made on product -- a computer. The only difference here is that Apple makes a computer for your desk, one for your coffee table, a mobile one for your lap, one for your palm, one for your wrist, and one for your TV. Maybe soon one for your car. And Apple could go on that way successfully for decades, just like Ford.
But Wall Street wants growth, and there's only one way to do that -- expand your market. And the folly with that is at some point, you've sold your product to every person on earth, and there's no more growth. So then you become a "value" company no matter how successful.
The only other way to achieve growth is to create a new product, which in Ford or Apple's case means, not an automobile, and not a computer. In the case of either, all of their products cannibalize from the other. Some people need a truck but not a coupe, some people need a phone, but not a desktop. Some people need both. Neither for nor Apple can convince customers they need more products than they need, and at some point, they just become a commodity maker, gradually expanding their base by converting customers from other brands, lowering margins until they maximize volume growth as well.
Perhaps Apple thinks wearables is stepping into the fashion world, but if they intend to become some kind of huge fashion house, they're off to a weak start. TVs aren't going to do it. Cars may do it, and certainly that's the most radical divestment from what they do now, but it's years away and hard to imagine any single automobile, or durable good, will spur the kind of growth Wall Street is looking for.
The reality is Apple created the right product at the right time and reaped the rewards. But it can't go on forever, no matter how well diversified. Just ask Sony. Or any consumer product maker for that matter. Apple can't continue to just repackage the computer into the product of the moment forever, once they've maxed their market share. So to satisfy Wall Street they have to come up with the product that everybody must have as well as the iPhone. And that's a hard trick to pull off, which is surely going to have peaks and valleys along the way.