HeliComparitor,
Your premise starts with "If the tanks rupture" so natrually you see no difference. The tanks are more likely to rupture when encased in the belly of the aircraft, that's why they have been moved to safer locations in more modern designs. The strong bladder tanks away from the crash impact zone therefore don't rupture, unlike those trapped in twisted metal with pumps still pressurizing all those lines beneath the floor.
If you factor in the 1,000 lb increased empty weight of the crashworthy seats that are an "option" on the 225 I think you will find where those lost passengers went. Again, if you chose to compare, it might be a good idea to use aircraft that have similar equipment. The Oil Companies do it that way, I believe.
Regarding operating costs, you are right, nobody knows how it will pan out, except that the S-92 has a maintenance "power by the hour" program for the entire aircraft, so the operator does not have to risk those costs. And the numbers being offered beat the older aircraft by a prtty big margin, I am told.