title is a bit misleading but i would like to know internally (what happens during ajax request) when i execute Code 1 and Code 2 in turns

Code 1

$.ajax({url:"1.aspx/HelloWorld",type:"GET",dataType:"json",contentType:"application/json"});

Code 2

$.ajaxSetup({
   contentType: "application/json",
   dataType: "json"
});

$.get("1.aspx/HelloWorld","",$.noop,"json");

i ask this because the method HelloWorld in page 1.aspx is executed correctly when run Code 1. But the seconds one refuses to invoke the pageMethod. I have set the ContentType and data as expected but the second request in Code 2 refuses to invoke the method does anyone have a reason for this ?