i get what i asked for. but 'round here we don't advise hacking the thematic core files. and i don't really even advocate creating a child header.php unless you are doing something really whacky.
you can do what you're trying easily from your child's functions.php
function kia_add_thumbnail(){
if ( ! is_front_page() ) {?>
<div class="header-image"><?php the_post_thumbnail( 'full' ); ?></div>
<?php }?>
}
add_action('thematic_belowheader','kia_add_thumbnail');
you will need to add another condition so it only will appear on pages and not on blog posts or archives