David Weaver
one of my early sets of japanese chisels (bought off of ebay) had convex backs. I thought it was a fault of low quality until figuring out that they can be controlled so that they don't dive past a mark, but still cut just as well.

There's too much literature out there already from wearing and others describing setting up paring jigs, etc, that need a parallel sided chisel and one dead flat on the back to convince many people to swim against the current, though.