Various rumour sites (including my own) have been following the progress. Despite what ThinkSecret says, the update still has to fix some issues and is not ready for prime time. It's currently just under 100 MB in size - but that's for the combo updater. Delta updaters will obviously be smaller.
My guess is they want to really, really, really make sure this one gets great. It's been in development for quite a while. "General stability" (whatever that means) is good for me in 10.4.2 as well as 10.4.3 - as long as I don't touch the known bugs that will hopefully be fixed soon. - I wait for a final judgement on 10.4.3 until that update is final.