Drupal 7 - access to page content in template.php
In page.tpl.php the content of the page is available in $page['content']. It seems that your are mixing two different concepts here: pages, any page on the site (including administration page, taxonomy terms page, and other not directly editable pages) and nodes, editable content. This can be rather confusing as a default Drupal installation provides a page content type. So you end up with page nodes, which are nodes of a the page content type.

The layout of the content of a page displaying a node, is handled in the node.tpl.php template. In this template, the body of the displayed node is available in $content['body'].

If you really need to access a field (handled using the Field API) of the node object ($node) from the page preprocess function in your template.php, you can use:

function THEME_preprocess_page(&amp;$variables) {
    $node =&amp; $variables['node'];
    $value = field_get_items('node', $node, 'FIELDNAME);
}