There has been a couple bits (its a pun, that someone will get), that the standard 6th edition starter Dark Vengeance has bene delayed. We don't know exactly why yet, but it does seem that on the GW site, the limited edition is sold out already. So while your local stores might still have copies, it seems the there just might be a gap between the limted edition and the standard one.
Frontline gaming did have a post up on the same subject, but I was unable to get it before it was removed, since I had no access to the internet today. Spikey Bits though still had his post up regarding a release push-back for Dark Vengeance, and Bols posted something similar today.
So it definitely looks like if you are wanting a set in the immediate future, to get yours while they last.
via Spikey Bits.
Here is the skinny straight from GW as they just informed their distrubitors, and trade accounts today:
"We've pushed the release for dark vengeance back. As soon as Dark Vengeance is available we will send them and notify you.
You can begin shipping Dark Vengeance to your customers as soon as you receive them.
They can begin to sell Dark Vengeance as soon as they receive it from you."
And to add insult to injury, the Limited Edition is "Sold Out" on their site as well.