I tested this example a couple of times and the Literal control that is added on every service request is updated and rendered with the respective value. You can see this on the following video captured
while running the example.
There is another project attached to this thread that uses a button click to execute a client side function that causes the XmlHttpPanel to update its content every 7 seconds. Please test it and let us know if the content changes are rendered on the screen.
If you still have problems with the example, please put together a simple running project where we can reproduce your behavior, and sent it back. Also, can you please provide more information about your project setup and the logic you are using?
the Telerik team