I'm not sure if it was last year or later but there was an article about Nintendo holding Wii parties.  At these parties influential women were asked to invite neighbors over to show off how fun it was to play the Wii.  Well Microsoft has now started doing the same thing by getting these mommy bloggers to host Xbox 360 parties.  

The USA Today recent has an article about how Microsoft is setting up theses parties in an effort to expand their base.  Microsoft has already captured the hard core gaming crowd with the Xbox 360 but now hopes to get the more casual fans by showing off their Netflix integration and their lineup of family friendly games.

I think if you look at how Rock Band is best experienced on the Xbox 360 or PS3 it makes sense to get people who would lean towards these casual games o their system.  You still can't download new songs to the Wii and with weekly updates why would you buy the Wii version.  Microsoft now has Lips, Scene It and the new Banjo Kazooie game on their system.  Microsoft is pulling a full court press to get the casual market and these parties will help.

Source: USA Today