The jars DO seal, just like any canned good. You don't have to refrigerate the jars, just keep them in a COOL, dark, dry place. I've been making cakes in canning jars for over 3 years and haven't poisoned anyone so far. Not only are the cakes tasty, they're very pretty to decorate. ANY quick-bread type cake cn be baked in canning jars.
Lighter cakes tend to fall once the jar seals.