(Alright don't throw stuff at me for what I'm about to say, it's just what I think, and I am a graphics whore so that would explain my answer, I just want to know if other people think this aswell)
I consider the Wii not part of this generation. Every generation seemed to be decided by graphics, that was always the biggest improvement every generation. Now I know the Wii has improved graphics over the GameCube, but compared to how different the PS3 is to the PS2 and X360 to the Xbox (or the HD consoles) the Wii isn't much of an improvement on graphics.
This generation we're in (the 7th gen) I consider to be the HD generation, so the Wii can't fit into that so I would say it belongs in the 6.5 generation.