Backwards compatibility history, as I remember it:
Handhelds
GB Colour, fully backwards compatible with GB, even added new features to old games.
GBA, fully backwards compatible with GB, just looked a bit stupid with the carts sticking out.
GBA SP, fully backwards compatible with GB, now even more stupid with the carts sticking out even more.
GB Micro, removed all backward compatibility, including GB games, GBA accessories and GBA power cables.
DS Lite, fully backwards compatible with GBA and DS
DSi, Nintendo pulled the plug on GBA and peripheral support, added region locking
3DS fully backwards compatible with DS games
Consoles:
NES 2 - fully compatible with NES, actually made it region free apparently.
SNES - no backward compatibility, except if you include the Super GB
SNES 2 - fully backwards compatible with SNES
N64 - no backward compatibility, except if you include the WideBoy
GameCube - no backward compatibility, except if you include the GB player
Wii - fully backwards compatible with GC
Wii Lite - no backward compatibility with GC
Wii U - fully backwards compatible with Wii