Because only people aged 18+ play games like halo and gears in the US?
The fact is that the Wii barely outsold the 360 in December of last year, it's not really much of a stretch to think that a much lower priced 360 will do better this year.
Do you really think nintendo is going to lower the price? Why would they?
I had a colleague that told me her son Played GTA, when i then told her that her son was fucking hookers and killing them afterwards she got a strange look on her face and i think she realized that it may not have been the best idea to give him GTA games.
The reason i think Nintendo could be playing with a price reduction is pure speculation, come Xmas and a little price drop it would yield lots of press and higher sales. And this december the 360 will be fighting a much stronger PS3 as well, so i don´t think it´s as clear cut.