Trying to change text via gettext filter but not working

I am trying to change the title of the Blog Subscription widget as the site visitors may be confused by the use of ‘blog’

I am using the ‘gettext’ filter. It work for strings in the twentyeleven and multiple other plugins but not Jetpack.

function cetns_filter_gettext($translation, $text, $domain) {
   if ($domain == 'jetpack') {
     $translations = &get_translations_for_domain('jetpack');
     switch($text) {
       case 'Subscribe to Blog via Email': // jetpack/modules/subscriptions.php
echo "<!-- CETNS_FILTER_GETTEXT: /$translation/$text/$domain/ -->\n";
         return $translations->translate( 'Subscribe to web site updates' );
         //return 'Subscribe to web site updates'; // Tried this - doesn't work.
         break;
     }
   }

  return $translation;
}
add_filter('gettext', 'cetns_filter_gettext', 10, 3);

The debug string is being output but the changed string is not displayed on the site. Am I doing something wrong?

http://wordpress.org/plugins/jetpack/