Yes, but that goes beyond the point. It is good to draw a line between task runners like Gulp or Grunt and bundlers like webpack or browserify. Bundlers do far less by definition. Even though you can find things like file copying plugins for webpack, it doesn't exactly excel there.
In practice a lot of people tend to use npm's package.json as a task runner for webpack. They define their tasks using the scripts section. Gulp and Grunt can be useful especially if you are worried about cross-platform support.
It's easy to write package.json scripts if you stick with Unix semantics for example. Writing something cross-platform is far harder due to differences (env variables, whatnot).