Apple took an estimated 83% of all app store revenues in 2010

"Though more online stores have been crowding the mobile app market, Apple remains by far the app-store leader, according to data out today from IHS, which recently acquired technology researcher iSuppli.
For 2010, Apple took in $1.78 billion in worldwide sales from its App Store, a leap of 132 percent from $769 million in 2009. And while it lost market share to some of its mobile rivals, Apple still captured 82.7 percent of the app store market last year, down from 92.8 percent the prior year."

Source:  Data from iSuppli, reported by CNET, 15th February, 2011