#3 - April 21, 2009, 10:16 p.m.
When a new, full version, World of Warcraft account is created the first 30 days are included. This same 30 day gratuity is currently not included with the purchase of expansion sets.
The expansion sets are just additional content for your full version account that has a fixed cost associated with it. When you purchase the Burning Crusade or Wrath of the Lich King you are paying for the additional continents, levels, quests and other awesome new stuff that was made just for that expansion set.
I do apologize for any confusion over the free 30 days and if they are included with the different game boxes, Peach, and I hope we cleared things up for you a bit :)