This example demonstrates how r.a.d.grid handles postbacks from other controls placed in grid cells. When you set EnableAJAX to true, the standard controls will make use of  the grid's build-in AJAX mechanism and make ajax requests instead of postbacks without any additional coding (basically RadGrid serves as Ajax container for them).
Even third-party complex rich-javascript controls can take advantage of the r.a.d.grid's AJAX mechanism by using the RadGridClientObject.AjaxRequest client-side method to fire asynchronous postback requests.The only requirement is for the controls to render their scripts inside their bodies.
Otherwise you need to set the EnableOutSideScripts property of RadGrid to true.
Further info about the usage of the RadGridClientObject.AjaxRequest method is available here:
How to raise asynchronous postback events