I'm young, highly qualified and unemployed. There's a lot of it about, oddly enough. I want to get a job developing software, and part of the problem is that my formal programming education is slim; so I need pieces of work to point to, an "I did that!" I am learning to write Android apps partly just to improve my skills, and partly to build up a portfolio of work which I can show to prospective employers.
Why blog about it? Self-discipline, primarily. If I know that the results are public, I have more motivation to push on through the debug phases, the design crises, etc. With the added possibility of showing the blog itself to people.
Why Android, not iOS?
1) I have an Android phone, and it's much more appealing to write an app I can use myself.
2) I have an Android phone, so I have a test-bed in my pocket.
3) Getting an app out on the Android Market (or Google Play, as it seems to be now) is a lot easier than getting one onto the Apple Store.
4) I just prefer the Android philosophy of an open platform.
Coming soon: Software and Tools.