IMPORTANT
This is not necessarily a bug. Primarily I am just trying to gather some additional information about different behaviour of AngularJs ($http) and Angular (HttpClient) APIs.

Please note that I've asked the same question on SO and Gitter but haven't received any answers so I decided to ask it there:

In AngularJs the default Content-type for JSON request is set like:

Content-Type: application/json; charset=UTF-8

This is the part of the AngularJs code that does it:

http.js

... and this is the commit in which charset=UTF-8 parameter was added:

angular/angular.js@10f80d7

Now in the case of Angular only

Content-Type: application/json

is used:

xhr_backend.ts

Side note:
We've noticed this when migrating from AngularJs ($http) to Angular (HttpClient).

Does anyone know why this difference?