On one hand, as I wrote here and Steven Sinofsky discussed in this podcast, moving to new devices and form factors involves new software experiences, and new software also often both creates and requires new business processes. It's hard to spend a day creating a 20-slide sales report on an iPad, even now that MS Office is available for iPad. But actually, that sales report should be a SAAS dashboard that takes 10 minutes to annotate. It will take time for those business processes to shift to enable more corporate tablet use.

On the other hand, the smartphone explosion is putting the internet into the hands of far more people than ever before, and it's alway there. If you're watching TV and want to know about an actor or a product, do you go upstairs and turn on your PC, walk across the room to pick up a tablet, or just pull a smartphone out of your pocket? The declining relative utility of the PC is reflected in a slowing replacement cycle (you don't replace the one you have) - the tablet has yet to make the sale in the first place, outside the initial wave of adopters.

Compounding this, the smartphone explosion is accompanied by an apps explosion. There are thousands of amazing apps on iPad (and very few on Android tablets, which is why the balance of use between the two is so skewed), but the smartphone opportunity is so much bigger that it attracts much more attention: there are more of these devices, some use cases make much more sense on them (such as Instagram) and some only make sense on them (such as Uber, Hailo or Lyft). So the smartphone experience now is very rich.

(A complicating factor, of course, is that these categories can't be neatly divided - phablets blur the boundary between phones and tablets and 'convertibles' blur the laptop/tablet boundary. But sales of both these are relatively small for now - even phablets)

A good illustration of this shift from the PC to mobile was Facebook's results this week: it now has more mobile-only than desktop-only MAUs and 79% of MAUs are mobile.