Issues with xml sitemap

I recently purchased an xml sitemap generator to use on a new site and was surprised to discover that there was a doubling up of urls. It appears that my CMS (Dreamweaver CS5) is outputting both an .html version and the non .html version of every url on my site.There is apparently something strange going on that relates to forwarding issues. Presumably there is an incorrect setting at work.

Naturally my initial reaction was to blame the sitemap generator, but I can reproduce the same problem using other generators. The site in question is www.cordless-phone-reviews.com.

Greatly appreciate any insights that may be offered. Thanks in anticipation.