I guess you never worked in Florida ;-)
I agree these LANs will do pretty well with huge DC and 60hz ground shifts but when you get short rise time transients like you see with nearby lightning strikes the only way to fix it is with copper. If we ran between different buildings or services with separate grounding systems we bonded them together. In some cases we even bonded individual machines together.
These are really those dreaded "ground loops" but as you say, these things reject that noise on the data side. This is actually a power hit that fries transistors. It may just be a regional thing tho. I don't remember this kind of thing happening much in Md
