Thanks to Peter Zheng at RiceHigh's Free Pentax Discussion Group, I've revisited the following two Japanese links to the sample images produced by the 40MP Mamiya 645DF:-
http://dc.watch.impress.co.jp/docs/review/newproduct/20091208_334045.html
http://dc.watch.impress.co.jp/docs/review/special/20090907_313117.html
via http://tech.groups.yahoo.com/group/ricehigh_pentax/message/738
When these are compared to the sample images from the Pentax 645D Beta, the difference is just like night and day! :-( (Even we just compare the small sized pictures - we have never seen any full sized Pentax 645D samples released and published so far btw! But WHY??)
How come this could be? The sensor size and pixel count of the two cameras are nearly the same, possibly with the same sensor used inside actually.. How come?? (I really scratch my head hard this time!)