6 months out is not an accurate statement, necessarily, but, as accurate as can be. It's more like a minimum of 6 months.
Once a year, discounted dates are released for the following year.I think it was around Oct or Nov last year, that 2002 discount dates were released. So, yes, you could get discounted ressies for more than 6 months, then. As the year has progressed, obviously, the time frame has gotten smaller, as new dates have not been released yet.
When the 2003 dates, as a whole, are released, we'll again be in the "more than 6 month ahead" time frame.
If you do book now, before the discount dates are released, you will be charged the deposit at that rate. It will be refunded or applied to the rest of your ressie (whichever you instruct) when you change the ressie to the discount rate.
Works just like the WDW hotels, only most of the time, you can book much further ahead at the discounted rates.