Clarify why a ViewModel should delegate data access to a service

Follow-up to [this issue](https://github.com/johnpapa/angularjs-styleguide/issues/181#issuecomment-67099471) where the issuer wanted code that would work.

What this pull request does instead is show with comments how many steps might be necessary for the view to do if it were to the job itself instead of delegating to a service.

None of these steps are things the ViewModel should know how to do.