Theme API feels to be incomplete

I try to create a small theme, without using any template files (think about more advanced Stark), just using style file and template.php. I am missing funcionality of theming 'Comments' title and 'Add new comment' title. They are hardcoded in the template file. When I want to add, say, number of comments in the comment wrapper title, I need to override comment.tpl.php. I digged into comment.module and I found, that theming the title is a matter of adding one more variable. Is this possible to extend the template in such way?

The new theme_comment_wrapper would look like this:

function template_preprocess_comment_wrapper(&$variables) {
  // Provide contextual information.
  $variables['node'] = $variables['content']['#node'];
  $variables['display_mode'] = variable_get('comment_default_mode_' . $variables['node']->type, COMMENT_MODE_THREADED);
  $variables['theme_hook_suggestions'][] = 'comment_wrapper__' . $variables['node']->type;
  $variables['title'] = t('Comments');  // Main title
  $variables['add_new_comment'] = t('Add new comment'); // Comment form title
}

And the template file:

<div id="comments" class="<?php print $classes; ?>"<?php print $attributes; ?>> 
  <?php if ($content['comments'] && $node->type != 'forum'): ?>
    <?php print render($title_prefix); ?>
    <h2 class="title"><?php print $title; ?></h2>
    <?php print render($title_suffix); ?>
  <?php endif; ?>

  <?php print render($content['comments']); ?>

  <?php if ($content['comment_form']): ?>
    <h2 class="title comment-form"><?php print $add_new_comment; ?></h2>
    <?php print render($content['comment_form']); ?>
  <?php endif; ?>
</div>

The thing I also miss is a similar functionality for 'Submitted by' message which is also hardcoded, but you can change name and date format in the template.php.

That would be great for theming to have ability to also override these messages in template.php. Then, you just not need to play with tpl files and use in your theme just style.css and template.php.

Any other variable can be overridden in template.php, am I right?