It would perhaps be better to post this in the appropriate forum (Javascript Frameworks).
JSON is just an optional part of the whole AJAX mechanism. AJAX a method for JavaScript programs to talk to the server and send and request data. JSON relates to the data format, not the page update architecture. You could use XML or grow your own data format and still be updating only portions of the page, on demand, as opposed to doing full page refreshes.
See also:
http://json.org/js.html
“Expert: a man who makes three correct guesses consecutively.”
Dr. Laurence J. Peter (American "hierarchiologist", Educator and Writer, 1919-1990)