1. Change Password and User Profile don't show the menu so the call is not needed.
The basic issue is that there is always a "CurrentPage" and the menu wants to show it as selected. The Url rewriting masks that the actual urls are like Default.aspx?pageid=x
If page id is incorrect or not specified in the url then the default page will always be returned by CurrentPage. So if someone is manipulating the url they will just get the home page.
So the menu doesn't know whether it is on a CMS page or not, it just wants to select the CurrentPage.
Pages that do not want this to happen should call this method to suppress the default behavior.
Note that not all non-cms pages need this suppresion, PageSettings.aspx and PageLayout.aspx are actually using the CurrentPage and it is appropriate for the menu to be selected at the CurrentPage
2. Might be nice but might also have a high ratio of effort to benefit, not a priority for me.
Joe