pickledamish, Fyrebyrd already linked to the post stating that there will always be at least 1 month delay from the official codex street date, but here it is again as you obviously missed it:
http://forums.wolflair.com/showthread.php?t=7454
While there is testing going on to try and iron out bugs before release, that is not the main reason why GK hasn't been released yet. DthShdw has hit it on the head - and Battlescribe's notificaton of GW IP infringement and a cease & desist last week may well have been excerbated by the inclusion of the GK list in that application 2 weeks ago. AB40k has had a minimum one month embargo on new codex inclusion for many years - some players do try to use the files as a way to avoid buying a codex and yet still using an army so the one month embargo may also help to reduce the risk of GW using this as a reason to shut them down.