A print of a page is not the same as a bookmark. Rather than a link to a point in time (which is what your print out is), a bookmark is a pointer to the latest version of a page. That has many benefits if the page is actively updated. The cost of that advantage is that it can fail completely if the page is taken down.

Ideally a browser should cache a page when you bookmark it and optionally refresh the cache when you revisit. That way, if you get an error you could look back at the cached version instead.

In fact, that'd be a damn useful browser plugin.