My understanding is that it is the initial screen of all default games. The only thing that changes is the bitmap covering the top half of the screen. If you remove games, you can safely remove this package too. I have done it without a problem, but then put it back because I decided I wanted mahjong after all.

No idea. I have removed it and hildon-welcome, as well as grepped for and deleted everything with splash in the name, but I am still getting the Nokia logo on startup, albeit not on shutdown. So your theory might be right.