After Apple's earnings call the other day, I had been planning to address the "disappointing" iPad numbers from Apple's most recent quarter. The good news is that MG Siegler has already done it, and I can just add a few of my own thoughts.

I absolutely agree with most of what Siegler says, except [emphasis mine]:

What we had was a perfect storm of events that led to the rise of the iPad:
The iPhone priming the public for iOS.
The desire for larger touchscreens.
And, of course, the implosion of the PC industry.
This is what led to 210 million units sold in four years.

I think it's a little bit too much to call the current—and pretty certain to continue—decline of the PC industry, an implosion. Implosion seems like too harsh of a term to me. The PC market is clearly retracting and being replaced by "post-PC" devices like the iPad and smartphones, but I think it still has a long future ahead of it, including actual growth in Mac sales. Maybe I'm arguing semantics.

Some other reasons why I think Apples Q2 Fiscal 2014 iPad sales were only 16.35 million, compared to 19.48 million in the same quarter a year ago:

The iPad isn't subsidized like the iPhone and other smartphones, so the replacement cycle for an iPad will be longer, maybe even much longer. It's much more enticing to get a new phone every two years when you can pay $199 or less on-contract for a flagship phone. When the starting price for a full-sized iPad is $499, it's a lot harder to justify a new one as often.
There are fewer reasons to upgrade your iPad with each new model year, compared to the iPhone. Aside from the iPad mini launching in the fall of 2012, which caused a pretty significant increase in sales, the full sized iPad hasn't had what many users might consider compelling-enough updates to cause them to replace their current model. The iPhone gets pretty significant camera improvements every year, and although more people than ever before are using their iPads as cameras, it's still much rarer for a person's main camera to be their iPad. Thus, I don't see iPad camera improvements, that also happen every year, being as motivating to upgrade as those made to the iPhone. Same thing for the huge CPU and RAM improvements the iPad has seen. I don't have any data to back this up, but I suspect that the main uses for many users' iPads are to watch video, read, surf the web and shop online. In my house we still have an original iPad, an iPad 2 and an iPad 3. I personally use a new iPad Air and absolutely notice a difference in performance, but my kids don't care or notice at all. The original iPad is still a very capable consumption device and my 3 year old daughter uses it every day to watch videos. The iPad 3 is actually still a great device. It runs almost all apps extremely well, unlike the original iPad and iPad 2, which can struggle or even not support some newer apps. Long story short, I think that many people are more likely to keep an iPad for 3 or even 4 years before upgrading.
Q2 of Fiscal 2013 was the first Q2 that included the iPad mini, and although the iPad mini with Retina Display that out in the fall of 2013 was a HUGE update, you could argue that many users didn't see the retina screen and A7 chip as enough of a reason to upgrade again after the iPad mini a year earlier. The first iPad mini's huge success was hard to beat a year later.

I think it's entirely plausible that we may still see two more quarters where iPad sales don't beat the same quarter from the year before. There are already 210 million iPads out there, and unlike many of their Android counterparts, I'd be willing to bet most of them are still in use. Again, I have nothing but anecdotal evidence to back up this, but I now a lot of people who have gone through a few Android tablets that are now either garbage or sitting in a drawer somewhere, not being used. Does anyone remember the Motorola Xoom, or the first Nexus 7? How many of those do you think are still in use?

I don't think the iPad's growth is anywhere near over yet, but the world may be catching its breath after 4 years of tremendous iPad sales growth. That's my prediction, but I guess time will tell.