Parameter less WebMethod and cache duration

Hi,

I wwant to cache the following webmethod (this is a test)1 [WebMethod(CacheDuration = 100), ScriptMethod()]
2 public static DateTime GetDate()
3 {
4 return DateTime.Now.ToString();
5 }

The point is I get always new result, I understood the response is cached with all parameters (I assume Url and posted data)...
So I do not undersand why I do not get always a different response.

Here is how I request the web method...
$("#getDate").click(function()
{

$("#content").addClass("loading");
$.ajax({
type: "POST",
url: "http://localhost:1118/Default5.aspx/GetDate",
data: & ...