There's a range of factors all coming together here: a (historically) worse selection of apps, a (historically) worse marketplace interface, a (continuing) lack of certainty as to how well apps will work on a given device, and a (significant, ongoing) deficit specifically in the high-volume game segment all push down Android revenues. (The early focus on free, ad-supported apps can't have helped either.)
If Android keeps selling as well as it does I do expect its app revenues will keep creeping upwards, and maybe get closer to parity, but some portion of that stigma will probably stick around forever.