Template themes which use the more recent format for the loop:

if (have_posts()): while (have_posts()): the_post();
…
endwhile; endif;

are more flexible and allow for easier adaptation than older style templates, using:

if ($posts): foreach ($posts as $post) : start_wp();
…
endforeach; endif;

Fortunately, a direct replacement of one control structure for the other seems to work seamlessly.