No. MMA goes through cycles where different styles work in different divisions. It isn't uncommon to have a number of fighters with similar backgrounds all winning titles. By the way, there are four BJJ blackbelts holding belts right now (JDS, Silva, St. Pierre, and Aldo), five if you count Barao... so... not really a substantive difference.
I wouldn't call those BJJ guys tho. JDS is primarily a boxer, Silva and Also are MT guys, and St. Pierre is a karate that guy that has developed into one hell of a MMA practitioner. The fact they have BJJ blackbelts doesn't matter to me its not what got them the titles per say. It has helped them keep the titles sure but they're not straight BJJ guys like Maia or Souza.