So? Both will explode. Gas will burst explode and may be a bigger explosion then petrol, but once it explodes it's done. Petrol however will explode and spread fuel which will continue to burn for awhile.
There is no logic reason to feel safer with a petrol tank than a gas tank.
Notice I said "splitting hairs". Pressurized gas is always going to be more inherently dangerous, and more like to "go off". If you're inside the blast radius of gas are you really going to care if a fire breaks out after the fact?