I started writing Android programs in 2011. With Android:
* I can develop the apps on Windows, Mac or Linux
* There is a lifetime developer fee of $25
* The source code is available
To program for the Windows phone, I believe I'd need a Windows setup which I don't have. "A small barrier" some might say, but a barrier nonetheless. I believe the Windows Store fee was $100 a year or something like that. Not much for a seeded company looking to build apps, but it might discourage a student looking to release an app.For all the hassles of Android's ever-changing API and such, they do try to make it painless for developers to get onboarded.