it seems like you are saying that to make reservations you can't just call once and say give us this week but rather you have to call day after day to reserve each day separately.
Yes, you can just call and reserve your whole trip at once. However, the earliest you can call is 11 months before the day you check out. So if your plan is to arrive on July 4, 2008 and leave on July 11th 2008, you could first call on August 11th 2007.
Now, before August 11th 2007, nobody can book for the night of July 10th 2008. So when you call on August 11th 2007, that will be the absolute earliest rooms can be booked, and it's very unlikely that all rooms will be sold out for the night of July 10th 2008.
However, people will have been able to book for the night of July 4 2008 since August 5 2007. Now, most of the time, the rooms you want won't sell out between August 5 2007, and August 11 2007. But if you are booking for a very popular time and want to be as sure as possible of getting your room, it makes sense to book day-to-day. Instead of waiting until August 11 2007 to book the whole trip, you book the first night of your vacation on August 5 2007, the second night of your vacation on August 6 2007, etc.
Remember, booking day to day isn't mandatory. It's only for the toughest to get reservations when you want to call at the absolute earliest possible moment.
Hope this makes sense.