These are different platforms:
* UI design is a lot easier on iOS if you use XCode's interactive designer. Doing it on Android with Eclipse's designer is painful, but I expect that Android Studio will make that easier.
* UI design without the interactive designer is easier on Android, because iOS is quite verbose for this
* About the code, I have found that iOS's APIs are badly designed, and change too often. The API's of Android are much more stable, but they can require too much code sometimes (example: setting onclick listeners for elements).
* About the tests, it is a lot easier to test for every iOS device, because there are so few (and iOS versions are rapidly deprecated). Android devices have a lot of different OS versions, screen resolutions, CPU, etc. That makes it tougher to test exhaustively.
Nevertheless, I have found that Android development is a lot easier than iOS development (at least for me), simply because XCode spends its time fighting me. For Android, I can just bypass Eclipse and work directly in vim with a Makefile, or I can develop in Scala and use SBT. It's much more fun that way :)
And to answer the last question: apps are primarily developed for iOS because:
* it is believed that iOS users are more likely to pay for an app
* journalists are often more on iOS than Android (and you want to please them)
* CEOs are often more on iOS than Android