> > even dumber, why carry around all the excess bulk and weight > of 645 body/lenses if the sensor is only 24x36?
Because that's what their target market already has in their kit. They can't get 'virgin' customers without any exisiting gear; the strength of the Canon 35mm line compared to Pentax means that most of the potential FF35mm customers would go to Canon. So Pentax need to play to their strength - the medium-format marketplace. They'll need a digital offering there. Nobody is talking about full-frame 645 sensors at a price point that would make sense for Pentax, but that doesn't really matter; for most professional use (as opposed to pure specsmanship) a smaller sensor delivers sufficient resolution.
