About DC3 Version 2.1 with XNA:
I can not see the purpose/benefit of this new version !
Of cause, basing the program on standard architecture is fine,
but from the user point-of-view, everything is almost the same.
The requirement of pixel shader 1.1 and vertex shader 1.1 made me think,
that this was a kind of 3D version of the game, which it is'nt.
you are right: this is still Diamond Caves 3 so no new features or a big 3D version of the game. It's just that more and more users of Windows Vista and Win7 were complaining that the game (version 1.16) would not run on their new system.
DC3 is now based on Microsofts XNA Framework which has a minimum requirement of shader version 1.1 although I am not using any kind of 3D objects.