Steven Peck, associated with the Drupal project, wrote about an article he came across regarding a comparison of the vBulletin forum and Drupal's forum. The article is titled, Goodbye vBulletin, Part 1: Reasons to Switch. The author of the article writes:

The aim of this article is not to poke holes, or say ‘vBulletin sucks’, but to provide constructive criticism of a successful product, proving that vBulletin is not always the best choice. In places the article compares vBulletin to Drupal, this is the platform The Webmaster Forums will be switching to and represents many of the things vBulletin should—in our humble opinion—aspire to.

Mr. Peck's reaction to the article (and my emphasis in bold):

Now this was a interesting. A well written article on why one site is switching over to use Drupal's built in forum rather then continue to use vbulletin.

In other words, Peck and many of us that pay attention to how the forum applications stack up against CMS native forums don't see too many articles like this. It is rare to see someone using a standard forum application such as vBulletin, SMF, or phpBB switch over to Drupal primarily for its forum functionality.