Re: A common API is definitely a must.
> Windows has always had a common API. It is called Win32.
You are obviously new to this thing called computers. Win32 did not exist on several versions of Windows. It started as Win32s, a limited version, as an add on to Win3.1. It developed in Win95, 98 and ME. A _different_, but almost compatible Win32 was written for NT but it wasn't until XP that the incompatibilities were mostly resolved.
Windows RT does not have the full Win32 API, it does have a limited subset and probably many incompatibilities.
> you can run a Win32 app written 10 years ago in any machine without any issues.
Simply not true for _any_ program. That is why Win7 has 'XP compatibility mode'. Basically an emulation of the WinXP Win32 API because there are differences.