It seems to me that USPS would blame any mishap on the sender to take the heat off of themselves, so I put very little stock in what they say on the issue.
Having worked at UPS, I know of mailroom and truck-loading antics and stupdity, and I don't believe that USPS would be any different.
No amount of bubble wrap will save a shipment if its placed at the bottom of the "wall" of boxes in an truck, or placed under an oversized/overweight (irreq or "e-reg" in ups terms) package.
Put that box under a vertically-positioned 7 foot weighty truck axle or 175 lb+ steel drum, and no bubble wrap will save it.
My lights have Lamda shaped cracks under the surface just from being on the truck (no collisions or anything). They aren't exactly the most durable thing out there.
Blame USPS.