I think its just moving Nintendo and Chat to a move inviting and personal tone. I mean you could be chatting with your grandma or something. I don't know. It just comes down to the, OOOO LOOOK SHINY! Syndrome. People always want something new and special to keep themselves entertained.

 the mii is an avatar that you create to represent you. some games such as wii sports will sport your miis body and face. in any of the wii sports games the mii you make and assign to your controller will appear in the game representing YOU. nintendos plan is to make it where you can assign a mii to your controller, go to someone elses house, load up a game on someone elses wii and bam your mii pops up on the screen. hopefully websites will feature special options such as the way alot of websites feature options exclusive to the psp and such. maybe JUST MAYBE some websites will allow certain options to use your mii on the web. imagine uploading your mii to your newgrounds.com account.....