Sitemap.xml and sitemap.xml.gz files are empty

I installed the latest Google XML Sitemaps plugin, and it installed without errors. I then uploaded empty the sitemap.xml and sitemap.xml.gz files and then activated the plugin.

The files stayed empty.

I currently have only two pages: home page, and a comment (email) page.

Later I attempted to manually rebuild the files, and the XML Sitemap Generator for WordPress 3.2.7 page reports that the search engines were notified, and it gives the time of the rebuild (UT/GST?) and reports below the location of the file.

So, I need to understand if this is supposed to be only for Posts and not Pages or was I supposed to add some internal formatting to the sitemap.xml file, or is the plugin supposed to manage that from an empty file?