One problem is price. The big sensor guys don't need to convince people who will never buy their products that they are better than the competition. They just have to win over the people who are actually in the market to buy and they do that more effectively by having face to face demos with potential buyers.
If dpreview buys all of the cameras they review (I doubt they do) then why should they spend 40 or 60 thousand dollars on a camera,digital back, and one or two lenses only to give a "Recommended (But only just)" rating? Hassey, Mamiya, and the others don't need that. They sell cameras just fine without worrying about what we, people who will never buy, have to say.
Secondly how could you compare a digital back only, to other cameras? I think the DXO "benchmarks" are a good way to do it but how could you compare a Hasselblad H4D to a Sinar arTec? Would it even be fair to say one is "Recommended" over the other?
I believe we will see a Leica S2 "Hands-On" preview since phil is a big Leica fan and it's more like a DSLR, but I don't think we will see a full on review. Maybe the "cheap" Leaf digital back will change things up a bit but I doubt it.