Originally posted by Winder APS-H is @ 1/6th the cost of FF.
APS-C is @ 1/10th the cost of FF.
Canon invented the APS-H format specifically because of the cost saving over the FF sensor. It was not just a random size they decided to make.
It's still a $5000 camera:
Canon EOS 1D Mark IV SLR Digital Camera (Body Only) 3822B002 B&H
If you're going to make a camera that expensive, then you might as well go FF and make a D700 clone. The cost savings, as the D700 and A900 indicate, are marginal between APS-H and FF.
Then there's a supply problem. Canon makes APS-H and Kodak used to make the M8 in CCD. Sony does not make APS-H. Maybe they could, but you'd have to pay a steep engineering premium (much more cost) to get it to market, wiping out the cost advantage.
What's needed is FF to be a price war between Canon, Nikon, and Sony, with Leica in the mix as well. That will drive down the price enabling a Pentax version. The economic rationale behind APS-H is probably history.
And on the note about the Fuji X100. This product is innovative, fore sure; but it treads on well-worn markets. It's the iteration of very popular rangefinders such as the Canonets, Yashica GSN's, and Olympus RC's (I own all 3). There was a lot of pent-up demand for these products remade in digital format. But price and lens restrictions make this a very difficult camera to compensate for the vastly superior flexibility of the SLR design. For what it does, I find it quite expensive.