All good in theory, but the problem is that the HTML usually outputted by these applications is a long way from standards-compliant or Search Engine Friendly (SEF), plus you have to actually purchase them, which for a decent one is probably going to be in the $50 to $100 range. If you have a dynamically served site that relies on databases and server-side code, you can also write (or otherwise obtain) code that spiders your site and generates a sitemap completely automatically.
This is a good method to use if you have a database driven site but could be considered over-kill if you have a relatively small site and again, you may have to pay for the code that makes it happen. All of these options have their good and bad points, but there is another method that you can use which takes the best of each of the previously mentioned methods and combines them to form a method of sitemap generation that works well in all situations.
Dan Wellman is an author and web developer based in the UK. Dan has written three books so far; the latest, jQuery UI 1.7: The User Interface Library for jQuery, was released at the end of 2009.