That is really impressive. However, this is an exception, not the rule and I've seen a number of old wooden houses in really, really bad shape when I lived in Sacramento. Even after 50 or so years. Of course, they have termite problem in California, that doesn't happen in other parts of the world as much.
You can to an extent, because the point is that the wood retains a sufficient carrying capacity for centuries to not fall down. I'm not saying a multistory building will survive for 800 years without maintenance, but that the carrying internal structure of a church like that can survive for 800 years is a pretty good indicator that it can survive for a long time.