Seems like every week somebody weighs in with a new study describing the size of the app market. World Mobile Applications Market reported in January 2011 that the mobile app market will grow from $6.8 billion in 2011 to $25 billion over the next four years. That same month, Gizmag.com reported that Gartner estimated 2013 app revenue at $29.5 billion. A month earlier, IDC estimated $35 billion in worldwide app revenue by 2014. Whatever number you want to use, it’s big.