How to attach css classes to the  title attributes if node_is_page() dynamically?
Okay, as commented under the question, I've tried out another idea: a little bit dirty since this is far away from the way it is supposed to be, but hiding '$title' in page.tpl.php and removing the IF NOT PAGE condition from the standart node.tpl.php (like in Bartik) makes it possible to access the title-attributes array, since node.tpl.php seems to know title-attributes, but page.tpl.php not...

But in this case I have to reimplement the programmatically "node is page OR node list switch" toggling of h1 and h2 again, since if-page $title in page.tpl.php did this before:

After removing the complete if-title-title part (in Bartik it looks like this, near the $content) from page.tpl.php,

&lt;?php print render($title_prefix); ?&gt;
  &lt;?php if ($title): ?&gt;
    &lt;h1 class="title" id="page-title"&gt;
      &lt;?php print $title; ?&gt;
    &lt;/h1&gt;
  &lt;?php endif; ?&gt;
&lt;?php print render($title_suffix); ?&gt;


... I have added (exchanged) this in the node.tpl.php:

//node.tpl.php

// usually we have something like the following here
/*
&lt;?php if (!$page): ?&gt;
   &lt;h2&lt;?php print $title_attributes; ?&gt;&gt;
      &lt;a href="&lt;?php print $node_url; ?&gt;"&gt;&lt;?php print $title; ?&gt;&lt;/a&gt;
   &lt;/h2&gt;
&lt;?php endif; ?&gt;
*/

// but we exchange it with this ...

&lt;?php print render($title_prefix); ?&gt;

  &lt;?php if ($page): ?&gt;
    &lt;h1&lt;?php print $title_attributes; ?&gt;&gt;
       &lt;a href="&lt;?php print $node_url; ?&gt;"&gt;
          &lt;?php print $title; ?&gt;
       &lt;/a&gt;
    &lt;/h1&gt;
  &lt;?php endif; ?&gt;

  &lt;?php if (!$page): ?&gt;
    &lt;h2&lt;?php print $title_attributes; ?&gt;&gt;
      &lt;a href="&lt;?php print $node_url; ?&gt;"&gt;
         &lt;?php print $title; ?&gt;
      &lt;/a&gt;
    &lt;/h2&gt;
  &lt;?php endif; ?&gt;

&lt;?php print render($title_suffix); ?&gt;


Now I do have my title inside of my wanted scope, where I can theme it programmatically inside the main content container. Thanks to Clive for his support on my question, and special thanks to Digidog from drupal.org, who gave me the final hint per mail.