WoW Wrath of the Lich King Content Patch

There was a content patch available right before Wrath of the Lich King was released, and there will be more patches in order to put more content into the game. Instances like the one in the Icecrown Citadel won't be included in the game until later. This is so some of the major battles of the storyline don't become trivial.WoW Wiki: Icecrown Citadel
Patch Fast Facts
1. There was a patch before the expansion came out
2. There will be more content patches in the future to include all of the Lich King content
3. Some content is released later to make the storyline more meaningful
4. The Icecrown Citadel Raid won't be released until the final content patch for Wrath of the Lich King
Content Patch Info

Part of the reason why Blizzard decided to release a patch before the expansion came out was to make sure there was a smooth transition in storylines. This way, the expansion will make sense when the rest of the WoW universe is taken into consideration.
There will also be parts of the expansion that are released in later patch updates. This is so some of the more important battles in the expansion don't become trivial right at the beginning of the release.WoW Wiki: Icecrown Citadel Some of the content that's released later will require players to be toward the new level cap, so players can level while waiting for the other patches if they haven't already.