I think most states/counties/cities are self-insured. If that's the case, they don't have an insurance company deciding breed restrictions. Private campgrounds can't afford to be self-insured so their insurance company makes those decisions for them.
And I'm with pconroy328. I would rather get bitten by a Pom than a Pit or Dobie. Have you seen Pits and Dobies bite? Pits hold on and shake, and Dobies bite in rapid succession. Dobies are one of my favorite breeds but I don't think I would ever own one. That has more to do with my own shortcomings as a dog trainer than a Dobie's possible aggressiveness.