Most of you are missing the point. If the FAA say that you should "inert" your tanks and you don't do it then, come any form of incident involving a fuel tank (it doesn't even have to be an explosion) the lawyers will slaughter the airline concerned. They finished off Swissair good style.
The seven years of grace are equally useless because if you have an accident in that period the lawyers and the juries are going to say - "Well you could have done it but you chose to wait."