Open any WiFi router configuration page or some page which asks for LDAP credentials and the password/login dialog appears in front of even when you have that tab opened but are currently on another tab. I would prefer or at least like to discuss the UX decisions/thoughts behind this decision since I like how Chrome has a better, non-interrupting UX of only showing that dialog when you are on that tab and not otherwise.

There's no UX discussion - it's clearly better if these dialogs are tab-modal. The difficulty isn't the UX, but the technical side of interrupting network loads with dialogs and having that not cause issues, IIRC. In any case, this is a dupe of bug 613785.