[Mythbusters]

the Windows Phone platform is going through some churn. With the new Windows 8, apps can share the marketplace so you can target the Windows installed base with your apps too. If you have already spent efforts developing the app, leaving it there seems worth it.

[jasomill]

Unless you build an app optimized for small form-factor mobile touchscreen devices, in which case much of the same Windows installed base will find it more convenient to use on their Android and Apple smartphones.