I think it is better to use the .htaccess file than tell your server to parse every .htm and .html pages.
I work for a webhosting company and we put the config so that all pages were parsed by php. Well it didnt take long when we got our first call complaining that their pages didnt work.
The reason was this little bugger in the start of the page:
<?xml version="1.0" encoding="ISO-8859-1"?>
You can propably figure out why their site didnt work. That will give an parse error for obvious reason. We offcourse could configure php in a way that it only parses php-code inside <?php ?> and not <? ?>, but that would mean a lot more phonecalls coming from our clients 🙂