Backpacker,
If you have a wet wing in a crash, it is almost certain that the tank walls (ie. the wing surface, leading edge, spar) will take some or all of the impact forces.
I think you put it better than me!
What I meant to imply is that the Cirrus uses a wet wing - The primary structure of the wing makes up the fuel tank. In an accident the primary structure is easily damaged and so a fuel leak is highly likely.
In my opinion, the double skin protection afforded by an aluminium (or even another GRP tank?) contained within the wing or fuselage has to be dramatically safer in the event of an accident than the Cirrus system.