The point isn't really that we're delaying Firelands so we can release ZA/ZG instead, or because we don't think players are ready for a new raid. Our messaging on the subject directly implies this, and that's our fault.
What we're really saying is that we want more frequent, slightly smaller updates to the game so that content keeps coming. Since Firelands isn't quite ready yet, we've made the decision not to hold back the other 4.1 patch content for it. Instead, we're going to release patch 4.1 with the content that's ready to go so the majority of players have more things to do, while also putting some finishing touches on Firelands so we can ship it out in 4.2 shortly thereafter. We're not arbitrarily holding back Firelands. On the contrary, we don't want to hold back other content updates for Firelands.
The main content features currently planned for 4.1 are:
- Zul'Gurub revamp
- Zul'Aman revamp
- New level-85 Stranglethorn quest line (phased) leading players into the troll dungeons
- New tier of Heroic dungeon gear (epic item level 353) to give players a slightly bigger boost going into raids for the first time
- New & updated flavor items, vanity pets, and mounts
- Guild Challenges (new guild quests)
All of this is in addition to a number of UI improvements, class balance changes, and more. We'll have more information on the patch 4.1 features coming soon. :D