Copying Angular project directory does not work?

Using Angular quickstart script is as follows:

git clone https://github.com/angular/quickstart.git quickstart
cd quickstart
npm install
npm start

When I do this, everything works fine. However, if I copy this directory to create a new Angular project:

cp -r quickstart angular-project
cd angular-project
npm start

an error occurs:

module.js:472
    throw err;
    ^

Error: Cannot find module '../lib/tsc.js'
    at Function.Module._resolveFilename (module.js:470:15)
    at Function.Module._load (module.js:418:25)
    at Module.require (module.js:498:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (/Users/username/src/angular/quickstart-test1/node_modules/.bin/tsc:2:1)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3)

even though tsc.js exists under lib/ in new directory.

Why does this error occur?

via Utku