would you rather have a repeat of Ulduar?
Horrible black holes and mega bugs, character eating zones due to an untested patch? No thank you.
The game has only been out for a month now. There's still an enormous amount of bugs (nothing out of the ordinary for a game this size) that need to be discovered and fixed. Adding an untested content update, with known bugs (which they stated in their note to everyone) would only compound problems.
We can only hope that BW manages to do something even close to Ulduar, which for me its the best raid even in WOW, for inmersion and content, followed by BT, Kara and SSC.