in my humble opinion the title "Preferred Applications" in the settings-menu is misleading, because what is really meant is more to set the *default* applications for the desktop. it's not a really big issue, but i think renaming it makes sense.
In Xfce 4.10 we will most likely add a MIME editor, allowing the default applications for all MIME types to be set in a single place: the preferred applications dialog.
thanks for your reply. it's great to hear that this feature is planned for 4.10, but to clarify: my bugreport was/is really about the *wording*, not about features ;)
For the mime stuff there is bug #6113.
Closing as wontfix for now.