Yeah, it looks like documents can be viewed publicly (without a Google account) if going through the Viewer: http://docs.google.com/viewer
Pretty handy if you have a bunch of files in their original formats available for downloading, but want to have links available for easy online viewing.
They probably haven't set up the sharing properly.
If you share a document, in the "Permissions" box the top item lets you change how visible a document is, and there's also an "allow anyone to edit" checkbox so you can even edit without signing in.
If setting it to public solves the problem, by all means do that!