Because the f/2.8's wide open DOF wasn't shallow enough for macro work to begin with!!!??
Yes, those were my first thoughts when I saw this in my inbox this morning. But i know someone is going to need/want it and buy it!
WM
I didn't think this one was going to be a macro though? I haven't researched it though at all so could be wrong.
Matt Granger also made the point that to get the same portrait composition with a 105 vs 85 you need to be further away. In such a case 85mm @1.8 would give a more blown at background that 105mm @ 1.4 shot from further back. I haven't tried either so I don't know how true that is.
Is your 200mm f/2 getting a bit heavy to haul around in your advancing years?