Why use foreach to get attachment_id if numberposts is equal to 1?

Question

get_children will return

an associative array of posts […] with post IDs as array keys, or an empty array if no posts are found.

This statement $attachment_id => $attachment is the same as the more commonly used $key => $value.

Using this command echo '<pre>'.print_r($attachments,true).'</pre>'; we get the following:
^{resumed version of a get_children with numberposts => 2}

Array
(
    [83] => stdClass Object
        (
            [ID] => 83
            [post_author] => 1
            [post_date] => 2012-06-22 05:06:22
            [post_content] => 
            [post_title] => barajas
            [post_excerpt] => 
            [post_status] => inherit
            [post_name] => barajas-4
            [post_modified] => 2012-06-22 05:06:22
            [post_modified_gmt] => 2012-06-22 05:06:22
            [post_parent] => 28
            [guid] => http://wp00.dev/wp-content/uploads/barajas3.jpg
            [menu_order] => 0
            [post_type] => attachment
            [post_mime_type] => image/jpeg
        )

    [180] => stdClass Object
        (
            [ID] => 180
            [post_author] => 1
            [post_date] => 2012-06-30 04:18:06
            [post_content] => 
            [post_title] => Yuri Atom_00281
            [post_excerpt] => 
            [post_status] => inherit
            [post_name] => yuri-atom_00281
            [post_modified] => 2012-06-30 04:18:06
            [post_parent] => 28
            [guid] => http://wp00.dev/wp-content/uploads/Yuri-Atom_00281.jpg
            [menu_order] => 0
            [post_type] => attachment
            [post_mime_type] => image/jpeg
        )

)

So, [83] and [180] are the $key and stdClass Object is their $value.
I think when calling get_children a foreach is almost mandatory, and this will be clear next…

If you use get_posts with exactly the same arguments, the result will be exactly the same except for one difference, the returned array will have numeric sequential keys:

Array
(
    [0] => stdClass Object
        (
            [ID] => 83
            [post_author] => 1
            [post_date] => 2012-06-22 05:06:22
        )

    [1] => stdClass Object
        (
            [ID] => 180
            [post_author] => 1
            [post_date] => 2012-06-30 04:18:06
        )
)

All that being said, if you use get_posts and numberposts => 1, you can substitue the foreach block for:

$thumb_for_pinterest = wp_get_attachment_image_src($attachments[0]->ID, 'full' );

With get_children we don’t know what’s the $key number, as it is the same as the Attachment ID, hence the foreach…

But with a regular numeric key (0, 1, 2, 3… etc), you can drop the foreach and call the first element of the array directly ($attachments[0]) and its object element (->ID).