A better way to think of the release cycles is like a mortar. At some point in the past, they could futz around with the mortar -- change alignment, direction. Then, they say, "ok, looks good -- let's fire this one". After that shell has left the chamber, nothing else going on is going to change where it lands. If you realign the mortar now, it doesn't matter -- the shell is already in the air. If you realize afterwards that you're a little off-target, the best you can do is make adjustments for the *next* shot. The mortar for update 12 probably got fired off about 4 months ago. If you have a really good idea right now, post it on the forums, and Eladrin loves it, it's probably not going to get "loaded into the chamber" until about the update 14 or 15 shell (which is probably the one they're actually aiming right now).
This is a little bit of hyperbole, but not by much. A lot of folks who've done a little bit of small-scale coding -- teams of 5-10 people -- can mistakenly assume that the last minute changes and decisions made on a small, agile team can still be done when you've got 40-50 people working on a commercial software product.