Note: Doing a Wordpress update every now and then is also useful for a website that changes rarely. With updates, Wordpress sometimes fixes some security critical bugs that might be critical even if you have user registration and comments disabled.
It really depends on your site. I usually have a static front page (instead of blog articles), but there's not that much that needs to be adjusted in WordPress.
If you don't want to update the site too often, try to use as few plugins as possible. Of course it's the right way to go in any case... WordPress core updates itself (within the major version, eg. 3.8.1 -> 3.8.2).