Why dragons then peaches?

In a lot of the traditional Japanese-style homes, I noticed that they have these dragons or some kind of imaginary beast on the four corners of the roof. They're quite fascinating.

My guess is that they're meant to protect the home from whatever evil spirits that may come from the four directions. That's a wild guess, so it could be that they're just for decorations.

But then, Japanese people are really superstitious in certain ways, so it's hard to think that these dragons have no meaning...

As you can see, some of them have a really menacing look.　

SO, my questions is:
What's the meaning behind a PEACH?

Why a peach? Why not a banana? Why not a whole fruit basket?

Ideas, anyone?