{*
the summary template has access to custom fields via the $entry->fields
hash
     and to categories via the $entry->categories array of objects.  Also
     attribute information is available via $entry->attributes.
     you should use the get_template_vars and the print_r modifier to see
     what is available
    *}

At the top of your default summary template (in your comment), you mention
$entry->attributes, but it's now $entry->attribs !