They also removed the Eberron backdrop article and added an article on non-evil drow (probably to take advantage of the FRPG release). My guess is that the changes were motivated by four things:
1. The issue was judged to be too long.
2. There was a significant revision to the Barbarian class that necessitated a delay.
3. WoTC wants to synergize with a product release.
4. They're going to start charging next month and the Barbarian playtest article would be a great incentive for people to buy into the subscription.
Personally, I think its a combination of several of these factors.