Has anybody actually had cabinets come off the wall from rough roads?
It seems to me that you would have stuff falling out of cabinets and getting broken/cracked long before the cabinetry itself would fail. I know I've had a few times where stuff has come out of cabinets, though not so much due to washboards as due to sharp corners or uneven pavement at intersections causing leaning side to side.
Naturally, rough conditions are harder on the structure and will lead to more squeaks and maintenance than glassy smooth roads.