I think, google has to find some other way to maintain its directory. We can find lot of issues and flaws in ODP / DMOZ. It includes the lack of dedication of the editors to maintain it, reservation of adding certain sites, Spurious attitude of editors who lists only their own websites, to list few. The result is so many dead links and un-updated categories.
Dmoz doesnt maintain "Google's directory". Currently Google uses Dmoz's directory. Chicken/egg thing. Not saying it's necessarily the way it'll always be (they've sorta buried it as Dmoz rep has deteriorated) but that is the current status.
Google is a business. If it wants a directory, it makes business sense to use the biggest one - particularly since it's free .
If they did that then they would need to change the guidelines to state that any sites that did not try to bribe for a listing would be banned