The drivers behind this take-off of mobile ad spending are:
Increased device ownership, particularly of tablets. Smartphone installed base growth in 2012 was more than 35%, while tablet installed base growth exceeded 120%. By 2016, tablet sales will overtake the sales of desktop and laptop PCs.
The intensity of online tablet use. Despite tablets representing less than 30% of the mobile device market in the US, they represent more than 40% of total mobile page views. In addition, the majority of tablet users watch video on their tablet, compared with about a third of smartphone users.