I would expect there to be fewer comments because it is more work to leave a comment now.
With Disqus you can leave a comment on the same page as the article, and you might hold a login cookie to Disqus across multiple websites that use Disqus already.
With BBS you have to click through to a second site, and create a new account at least once. (Though Discourse supports Google, Facebook, Twitter etc logins.)
But BBS is also a legitimate community, intentionally separate from BB proper, where you can create your own topics and have discussions as long as you like, not just for 5 days after publishing. It is like adding a wing to the mansion, if you will.
