It was Steve Jobs' last magical gadget: the iPad, harbinger of the future. 

The iPad went into the tablet space, which was like the moribund corner lot where no restaurant can make it for more than a month, and transformed it into a viable market. The laptop PC trembled before the convenience and portability of the iPad. 

But then a funny thing happened: iPad sales growth began to slow. And this quarter, sales substantially declined from the second quarter of 2013. Back then, Apple sold 19.5 million units. Today, the company reported that they'd only sold 16.35 million. 

That's far below the average of 19.3 million units that analysts were expecting. Only one of the 34 analysts surveyed by Fortune, Matt Lew of the Braeburn Group, missed low (with an estimate of 15 million). Every other analyst missed high. 

And just to show that it's not only one bad quarter, Andreessen Horowitz's Benedict Evans posted this chart.

The iPad simply isn't displaying the kind of growth that the iPhone continues to show.

So what's going on? There are a few interrelated theories:

  • The iPad market is saturated. Tablets are gadgets for a largish, elite niche. So, as a technology, the iPad adoption curve might look more like a bicycle's than a mobile phone's. Some people have and love them, but not everyone needs one.
  • Tablets are "tweeners," not as robust as a computer nor as convenient as a phone nor as fun as a gaming console. And because many people in developed countries already own those other gadgets, the number of people who really want an iPad is not that big.
  • Actually, it's just that people don't need anything bigger than a big phone. Perhaps this is rightly a subpoint of (1), but it may just be that high-quality, 4-5.5 inch phone screens are good enough for most purposes. (The shorthand version here is: Phablets win.)
  • The upgrade cycle is more PC/TV-like than phone-like. People get new phones all the time, but maybe they refresh their iPads once every three to four years.
  • Who needs iPads for Facebook? What do people do on their mobile devices? Facebook and Twitter. For that, a phone works great. A more general way of putting it: there aren't enough awesome apps that require a tablet.

I'm not a doom-and-gloom anti-tablet futurist. However, I will say that the enthusiasm that tablets were generating in 2010 and 2011 at media companies has evaporated. The best mobile strategies are ones that emphasize phones and Facebook because the expected flood of tablet users never showed up. At The Atlantic, we've seen an explosion in smartphone traffic while our tablet views have held steady for a long time. I've heard the same is true at many other media brands. 

But let's not get tooooo carried away. Apple still sold more than 16 million miniature computers. Worldwide PC shipments for all manufacturers and operating systems combined were only 76.6 million last quarter, and iPads easily outsold any given PC maker's total product line by millions of units.