Based on the discussion so far, it seems the reasons for modding either is:
- People mod SH3 because they love the game.

- People mod SH4 because they want to love the game. :p
You mod a game because you can. It's a way of taking a game experience and truly making it your own.
Modders represent the dreams of all those who have ever played a game and said to themselves, "I'd do that differently." or "I can make this better."
I could only wish I had even some of the skills of the likes of BBW. He carries on his shoulders the hopes and imaginations of every u-boat kaleun or submarine skipper.
So few have given so much to so many.