Why, when installing modules, many other modules are installed?

Question

Node.js

When installing any module on OS X, the node_modules folder contains only the modules I installed, but when installing any module on Ubuntu, for example "npm install express", a lot of things are installed:

accepts              depd              json3              range-parser
after                destroy           media-typer        send
array-flatten        ee-first          merge-descriptors  serve-static
arraybuffer.slice    engine.io         methods            socket.io
backo2               engine.io-client  mime               socket.io-adapter
base64-arraybuffer   engine.io-parser  mime-db            socket.io-client
base64id             escape-html       mime-types         socket.io-parser
benchmark            etag              ms                 statuses
better-assert        express           negotiator         to-array
blob                 finalhandler      object-component   type-is
callsite             forwarded         on-finished        ultron
component-bind       fresh             options            unpipe
component-emitter    has-binary        parsejson          utf8
component-inherit    has-cors          parseqs            utils-merge
content-disposition  http-errors       parseuri           vary
content-type         indexof           parseurl           ws
cookie               inherits          path-to-regexp     xmlhttprequest-ssl
cookie-signature     ipaddr.js         proxy-addr         yeast
debug                isarray           qs

Why?

Answer 1

module dependencies probably...