That's true. I am a part of a forum called Bitcointalk (I am not active though). It is build on SMF and it is the largest forums I have ever seen (apart from Reddit and Quora). Software is just a frame work, it is your niche and content quality that really matters. However, for most of us becoming successful with free software is very difficult. I ran a SMF forum for two years and yet I had less than 50 members and 1000 posts. Two months ago, I moved to Xenforo and now the forum has hit 3k posts.