Fundamentally, Drupal is a great SEO friendly platform. With the right information about how and where to tweak Drupal for SEO, you can have a lean, mean SEO machine that outperforms and out-competes your competitors.
Having relevant content (in the form of high quality comments) added to your webpages on a regular basis, without having to manually create it, is a great advantage over competitors who don't implement commenting features and don't turn their sites into a hive of content producing activity.
Even on a decent CMS platform like WordPress or Drupal, administering comments can be a bit of a pain. More than likely, while you're starting out, most of the comments you receive will be spammy garbage that can't be published to the site.
Having a flexible, powerful and reliable web platform is one of the most important aspects to any new Internet based endeavor. The Internet is teeming with super easy to use online blog or website builders that can get a reasonable looking, basic site or blog up in a matter of minutes. We've certainly come a long way in the last 10 years in this regard.
However, with simplicity and ease-of-use, there is always a trade off. What you make up in simplicity you often lose in flexibility and power. A good example of this is hosted WordPress sites. WordPress is a fantastic web platform for bloggers, and the hosted version (http://www.wordpress.com) allows anyone to run their own blog without having to worry about hosting and server issues.
While Drupal is, on aggregate, one of the best web platforms around, there's always room for improvement.
Drupal 6 has one fairly important failing when it comes to files and file handling. During site configuration you are required to decide whether or not files are downloadable directly by the public or whether Drupal should maintain control of the downloads.
This is/was a fairly inflexible system and one that led to further problems down the line...
Being able to accurately control the size and dimensions of images is vital for any modern website.
Nowdays, different media types are commonplace because broadband has become ubiquitous. Because of this, websites have the opportunity to show off far superior and more interesting pages to the average visitor.
But being able to handle images on the fly is not something that is necessarily too easy to do - unless you have a well designed web platform.