However, one of the core keys of B4* family that makes it a RAD platform
is that its syntax is almost identical to Visual Basic.
You can develop in VB.net for windows Phone, and as far as I saw its not really
that hard at all to learn to develop for WP.
I'm planning to upgrade to Win 8 to start developing for Windows Phone in the
near future. And I will then be able to develop for Android (with B4A), IOS (B4i)
and WP8 (VB.NET), and I will rule the world, MUAJA!
This statistics represents shipment, but doesn't mean that the retention of a windows phone might have been higher (maybe the one who had a Samsung s4, wanted to go for a S5 this year, and maybe the one who had a high end Nokia Lumia didn't need the change).
However, 2.5% worldwide its a lot, its millions of users! I know its 40 times less than Android, but again there are a lot of developers that thinks "meh, I won't go for the windows phone market because its too small", so the competition in this market is also lower. What is more, Microsoft is a big boy and won't let Windows Phone die any soon. The Windows 10 release will be a big change, you will be able to develop for both desktop and mobile and go to a single Market, so you will hit the Desktop Store as well.
And keep in mind, that if one day you want to sell some app to a client, you will get more reputation if you can provide a complete mobile solution: Android, WP, and IOS (let assume that blackberry its really going down soon ). You will be able to program in one language (visual basic), and prove a complete native solution for all platforms!