You don't need a package.json to use CommonJS or even to use Browserify, but as a developer I don't want to copy external dependencies into a vendor folder to use them, I want to declare my deps in my app's package.json -- so any lib that uses CommonJS but doesn't provide a package.json I will probably not bother to use.

People who use npm packages in browser code are pretty much all using Browserify or Webpack and leverage npm. (Many people use Bower, but I don't see the point of using two overlapping package managers.)

It's a new dawn of modular JS code; no more global namespace, no more stuffing CDN links in your <head>. I recommend giving it a go.