Wide-angle: the Achilles' heel of SLRs?
Nikon came out with an excellent wide-angle lens, similar to the Zeiss Biogon in design (although with a slightly reversed formula), which you can see at http://www.mir.com.my/rb/photography...wides/21mm.htm .
Unfortunately, this gem cannot be used on any but the more pro-line cameras, that offer MLU. That negates the "reflex" advantage, requiring a separate viewfinder and zone focusing.
While this neither confirms nor defeats the "Achilles' Heel" premise, it does allow for an adaptation that works.