Why is the Win32 boilerplate the way it is?

[Vladimir Panteleev via Digitalmars-d-learn]

On Sunday, 29 June 2014 at 15:06:25 UTC, Jeremy Sorensen wrote:
> The only question I have is what happens when you use 
> SUBSYSTEM:WINDOWS:4.0 (Which I understand means XP or higher) 
> and the program runs on something older?

Windows XP is version 5.1.
4.0 was Windows NT 4 (which I believe was the NT-family Windows 
version preceding Windows 2000).