Angular CLI dependencies - why do I need to install @angular/router if I don't use it?

When I start a blank Angular CLI project, these dependencies from package.json look like not necessary, so I'm trying to remove them (as well as removing FormModules and HttpModules from imports):

@angular/forms": "^4.0.0",
@angular/http": "^4.0.0",
@angular/router": "^4.0.0",

But when I try build the project, I'm getting an error:

'ERROR in Could not resolve module @angular/router'

And what looks even more weird to me, after re-saving a file the project rebuilds successfully and it works.

Can somebody explain where is this hidden dependency from @angular/router?

My files:

app.modules.ts:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';    
import { AppComponent } from './app.component';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule {}

app.component.ts:

import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  template: '<h1>test</h1>'
})
export class AppComponent {}