Pooh, as luggage is invariably located further back than a pillion could sit (especially if a top box is fitted) any weight in this area will stress the subframe far more than the pillion (leverage effect) also stuff in the luggage will bounce around more than a pillion, meaning that I wouldn't be surprised if the shock loadings to the subframe from 50lbs of luggage rattling about are far greater than that of a 200lbs pillion with their built in shock absorber (arse)
The sort of Alloy used for the subframe is quite stong if loaded slowly shock loading quickly cause fatigue and failure.
I hope Suzuki get to the bottom of this quickly, the amount of times I've gone round 130MPH + sweepers with the doris on the back is enough to make me feel lucky to be alive!