Hi Aaron,
omitting the PHP closing tag is a tip to avoid trailing white spaces to be streamed as output in the browser, which could be an issue when HTTP Headers must be sent. Rif.: http://framework.zend.com/manual/en/coding-standard.php-file-formatting.html.
I'm always used to close tags and take care not to add whitespaces after the closing tag... but for quick fixes it helps not to add new issues ;)
Ciao,
Matteo