If you needed more evidence that Android and iOS are crushing the competition, Nielsen has come out with some numbers today showing just how entrenched the rival operating systems are in the U.S. market.

Nielsen’s third quarter State of the Media: The Mobile Media Report found that 83 percent of all app downloads happen on Android or iOS devices. 

The two platforms continue to duke it out for market share, with Apple holding 28.6 percent of the smartphone market and Android at 44.2 percent as it leverages the advantage of having multiple manufacturers, which help get a larger variety of its devices into carrier’s device lineups. 

Research In Motion’s BlackBerry platform continued to see erosion with a 17 percent market share. Windows Mobile and Windows Phone 7 clocked in with a combined market share of 6.3 percent and Symbian held just 1.6 percent of the market.

The meteoric rise of Apple’s iPhone and Android-based devices comes as smartphone ownership has more than doubled in the past two years. In 2009, just 18 percent of wireless customers had smartphones. In 2011, that number hit 44 percent. 

Customers between the ages of 18 and 34 continue to lead adoption, with smartphone penetration among users aged 18-24 standing at 53 percent. About 64 percent of wireless subscribers aged 25-34 currently use smartphones.