主要区别是：dialog默认含回退按钮。并且dialog在1.4版中已经过时，1.5中将会移除。
下面是
原文1：
Using a Dialog Window as a Popup
A jQuery Mobile dialog window can also be used as popup window. The main difference between a dialog window and a popup is that a dialog window typically requires some sort of feedback in the form of a button interaction, for example. A popup window can contain anything[md]for example, an image gallery, video, copy, and so on.
原文2：
Dialogs are deprecated as of jQuery Mobile 1.4.0 and will be removed in 1.5.0. The dialog option provided by the page.dialog extension of the page widget allows you to style a page as a dialog, however, the special navigational handling will be removed. You may also consider implementing dialogs using popup widgets.