Access model data throught req.body after a fetch() call

I would like to know if i do something wrong or if it's normal that i can't access the properties of my model on the server side (using express) by calling req.body.username (for example) after a fetch() call:

app.get("/test", function(req, res){
  console.log(req.body.username); //Undefined
});

But i can access it the same way by a PUT request.

Actually i used the url to send the username but i would like to clean my routes and access the properties throught req.body instead, (of course after setting it in my model on the client side).

Thanks for the explanation !

UPDATE:

In case it could matter, here is my app configuration:

app.configure(function(){
  app.use(express.bodyParser());
  app.use(express.cookieParser());
  app.use(express.session({secret: 'test', store: express.session.MemoryStore({
    reapInterval: 60000 * 10
 })}));
});