Well ... that is not entirely true. From what I understand, the deal is that any patches on the official builds need to be reviewed and approved by MozCorp to use MozCorp's trademark. The delay that this would present was not acceptable to the Debian folks. MozCorp is trying to build a brand and don't want any old binary floating around sporting the trademarked name even if the binary floating around might be better than their official one. Debian's issue with the review policy is largely speculative (since one would think that MozCorp would be interested in patching security holes in their own product just as much as Debian is) but it is appearently one that the RH/Fedora engineer (Christopher Aillon) working with the Mozilla Project shares based on this comment on the devel list:
... and why I mentioned that they will have to deal with lots of comments from the Iceweasle-brigade.