They are sometimes not accessible for technical reasons. WWW sites should be judged not only for their content but also for design, technical quality and functional structure. New quality criteria seem to be necessary. Guidelines to design effective and user-friendly websites can be found in many journals and on the net.
Different approaches define quality criteria from the perspective of the creator and the user.
One example can be found at Berkeley Digital Library . More detailed information about construction of quality online resources is available at the homepage of Matthew Ciolek , an expert in this field.