Their entire approach to raid testing and class design/balancing seems to indicate that they are being a lot more measured and careful with raid and class design and balancing this expansion than they have been in the past. I don't think I remember Ghostcrawler ever being as active in interacting with players in regards to class design (at least not since maybe Wrath development). I also don't think the Cata raid testing was as extensive as what we are seeing now (and we aren't even halfway through it).
Maybe they figured that they got burned by Cata (class balancing and raid design was a mess at launch), and burned by D3 launching with all kinds of unresolved issues, and they want to slow down the cycle and make sure they have it right before releasing MoP. That theory seems to lean to a release date somewhere between October 2nd and October 30.