I think is quite useful being able to call `getString` directly. Fragments and Activities also expose this method even though you can do `getContext().getString(...)`. Ideally other helper methods should also be included but there are quite a few of them and they aren't used as  oftern as `getString`. 
The other reason is that these methods make sure that the `Context` is not null so you don't have to do that check in your code. You just call `getString(...)` and don't have to worry about anything else.