I think you mean it's successful because of its lack of rules, and I disagree. WordPress's low barrier to entry stems from a combination of PHP's ubiquity and a positive feedback loop of popularity. More rules wouldn't hurt either of these factors.
More like PHP's ubiquity which leads to easy installs for non-developers. The reason wordpress is so successful doesn't revolve around the devs. It's because your everyday blogger can setup a blog in 20 minutes. The dev focus comes from having so many users.
