jquery.ajax({cache:false}) - why not use HTTP Cache-Control?

jquery.ajax({cache:false}) - why not use HTTP Cache-Control?

Does anyone have any insight on why jQuery uses the timestamp query param trick,
instead of sending "Cache-Control: no-cache" HTTP header,
when making an AJAX request with the cache:false option ?

I'm interested in the historical/official reason, but feel free to speculate on why you would think of doing the same.

Thank you
*curiousity killed the cat*