Why this choice of ordering pictures?

You can Suggest it at the Dev Site.

Otherwise, you can also Do it yourself. Open photogallery.php and find this Line :
[syntaxhighlighter brush=php,first-line=1,highlight=0,collapse=false,html-script=false] $result = dbquery(
"SELECT tp.photo_id, tp.photo_title, tp.photo_thumb1, tp.photo_views, tp.photo_datestamp,
tu.user_id, tu.user_name, tu.user_status, SUM(tr.rating_vote) AS sum_rating, COUNT(tr.rating_item_id) AS count_votes
FROM ".DB_PHOTOS." tp
LEFT JOIN ".DB_USERS." tu ON tp.photo_user=tu.user_id
LEFT JOIN ".DB_RATINGS." tr ON tr.rating_item_id = tp.photo_id AND tr.rating_type='P'
WHERE album_id='".$_GET['album_id']."' GROUP BY photo_id ORDER BY photo_order LIMIT ".$_GET['rowstart'].",".$settings['thumbs_per_page']
);[/syntaxhighlighter]

Now see :

GROUP BY photo_id ORDER BY photo_order

Change it to :

GROUP BY photo_id ORDER BY photo_datestamp DESC

[ Moved to Modifications and Requests ]