Who's to say that there will be a replacement iLife offered in January? It only makes sense to make fewer releases as a product matures....There's no way anybody's going to pay $70/piece for software that will be outdated in 6 months. Even a release date as late as April or May is pushing it.
OS X has only reached the .9 stage once before, so that theory is not based on any repeat occurrence--they don't "typically" do anything of the sort. Incidentally, the compatibility version I've found to be most common is 10.3.8.3. Typically, Apple makes the .9 version the latest version they support and works with all updated software they make (i.e. the majority of Apple software requires 10.3.9 or higher).
I am certainly in agreement with ehurtley and others--the consistent and untouched bugs in the developer builds clearly suggest that efforts are being directed elsewhere internally. The Finder has quite literally been untouched outside of quick look, and new Finder technologies were heavily intimated around WWDC last year and I think they may have even been mentioned at Macworld. It's clear also in some cases that test code was piled onto existing software for development purposes and doesn't reflect a finished product. I can't discuss this in any detail (but also will freely admit that I am not personally involved with this round of beta software).