If you measure it alone one dimension - for example social or economic ideology - then moderates rule, but reality is more complex. The political world not contains your standard liberals and conservatives, it also contains libertarians, populists and moderates. The former two complicate things. Libertarians are liberal on social issues and conservative on economic issues, populists are the reverse. People may be moderate on economic issues, but extreme on social issues, or vice versa. People who are moderate on both social and economic issues are very rare.
This graph purports to explain that fact: