I'm currently reading The Bicycle Wheel by Jobst Brandt, and I'm reading all of the issues with offsetting the rear rim toward the drive side of the hub...
Asymmetry in a rear wheel built for a multispeed gear cluster makes it weaker against side loads coming from the right side. This means that the wheel bends to the left more easily than the right. The greater the offset, the weaker the wheel. In order to reduce offset for six-, seven- and eight-speed clusters, hubs have been built with narrower flange spacing. Although they reduce the disparity in tension between left-side and right-side spokes, they weaken the wheel against lateral forces.
So, I'm curious, why is it the standard to do so? Why not center the rim to the hub just like the front, and then offset the frame's drive side rear triangle to accomodate the difference? It may shift the chain line a bit, but this doesn't seem like anything that challenging to adjust for. The strength and durability benefits are huge, and the only downside I can see is that you couldn't arbitrarily change rear hub widths (not that it seems they change that often anyway), or you may have to introduce the offset again. Why don't bicycle manufacturers start doing this instead? Do they make frames that you can use a rear wheel built with the rim centered on the rear hub?
Rear Wheel Offset -->