According to a blog note by Andreas Barth, Debian developer and release manager, the delay has resulted because "Some people who used to do good work reduced their involvement drastically. There was nothing I could do about, and that happened way before I started full-time on release, but on the global picture that still counts."
It appears that these developers have pulled back from working on Debian because of their objections to Barth and fellow release manager, Steve Langasek, being paid to work on Debian by the Dunc-Tank.org.
Dunc-Tank.org is a group of Debian developers that set about raising funds to be used for "financially supporting the volunteers working on managing the release process, allowing them to devote their full attention to that task."
Specifically, the groups goal was to raise enough funds to pay "both release managers enough to work exclusively on the release of etch for a month each, having Steve Langasek available full-time during October and Andreas Barth available full-time during November, with the release expected to follow soon after in the first week of December."
The group wanted to do this because Debian has a long history of being late. That, in fact, is one reason why the Debian-based Ubuntu distribution was started.