I've built many wheels with these hubs. I used one for the rear wheel of my Rambouillet way back in the precambrian epoch. I much prefer the tight fit of the spokes on those hubs to the sloppy fit on most hubs these days. When the spokes are tensioned, they conform to the shape of the hub flange, and then there's no further movement of the spokes at the flange. No movement means no work hardening of the steel, and no breakage as the spoke becomes brittle from that hardening.
I don't know why Shimano made the right flange wider than the left, but it's certainly nothing to worry about. The difference is about .2mm. These hubs have been around since the mid 1990's. Mine is still going strong.