It's more so the testing aspect. The earlier we release content, the faster we can have 9k people testing it, and catching bugs faster. My theory is also that releasing content earlier will lead to bored people earlier, and it will push developers to get more things released earlier. Now the question of course would be where the bottleneck in development occurs (developers can't push out content faster) leading to a decrease in quality, and faster rush to ICC 25 hc. Once ICC 25hc is out, the other servers will then want the port, and to please them, you will be required to port.
I suppose my theory really comes out based on past experiences, albeit the server was headed by someone different at the time. Firelands was released, not because it was ready, but because people were bored. Dragon Soul was released not because it was ready, but because people were bored. MoP was release not because it was ready, but because people were bored. You get where I'm going... :)
edit to expand:
With that said, perhaps it is wrong to judge Warmane in the same way, but so far, Lordaeron has followed the similar path. TBC wasn't ready, but you still released it, and it seems the same will happen with LK. My school/work revolves around pattern identification, and you can't deny the pattern is continuing. And to be honest, I don't disagree with that pattern. It is, I have found, the optimal release method for private servers. Private servers need constant releases to keep the population going (specially when so little works). You can't wait for 100% working things to release, because by then, you will have lost a significant portion of the population (MoP being a clear example). The aim is, new releases will bring new players (hopefully, and if our competition is weak) which is why you release first, and polish later.