The XML submitted to Google is enough.
Usually the sitemap.html is for the user only. In some cases, when you don't want or you don't have access to the webmasters tools to submit the XML, is easier to put it on the sitemap.html.
The idea with this file is to let Google know about your files that make your site and you need G. to crawl. If you have a good site-link structure, you don't even have to submit an XML to Google. He is smart enough to find all your pages.
If you have some pages that you don't want Google to index, just put them in robots.txt file.