I perfectly know how many cows MS happily milks with Gold, but as Greenberg said they'll increase value for money AND they'll keep XB360 $100 cheaper, and paying an additional $50/yr fee what others offer for free would deny both points, I won't question his word, particularly as he'll have to keep it if he want to lift again sales.
Edit @CaptDS93: maybe in USA, but last time I checked, in Europe the best price you can find for Live Gold is full price.