In contrast, tablets still seem modest in their penetration and poised to take a lot of the market for desktops. Microsoft in the most recent quarter doubled Surface tablet revenue to $893 million from $400 million, while citing "continued softness in the consumer PC market." BuzzFeed, for example, gets more than half its traffic from mobile devices, but within that number, less than 10 percent is tablets.
In the U.S., eMarketer puts smartphone penetration at 74 percent, compared to tablets at 52 percent.
(Read more: Apple drops on weak iPhone sales, revenue outlook)
With that said, I think we'll continue to see more and more web usage coming from phones, especially as Android improves its user interface and ease of use.
Combine these trends with rumors of larger screen "iPad Pro" (12.7 inches compared to today's 9.7 inch screen) that will serve as a work device, and you start to see just how much headroom there is in tablets compared to phones— and certainly compared to desktops.
Further complicating this is the move to larger phone screens. The current iPhone has a 4-inch screen as compared to the Samsung Galaxy S at 5 inches, and the Galaxy Note at 5.7 inches.
So there is a fair amount at play in terms of form factors as tablet penetration grows. On the next upgrade cycle, will buyers choose a single phablet (phone tablet) in a larger size of say 5 inches? Or will they chose a 4-inch phone and existing 7.9-inch mini or 9.7-inch iPad to pair with it? And how will the new generation of Pro-size tablets figure into this mix?