Windows Live Mail, Virtual PC, Jeyo (when phone not connected), Speedfan
originally didn't had that option either, there are some more but can't
remember them all as I don't have them all installed myself. uTorrent puts
itself in the Notification Area and by default unloads when pressing Close.
I believe QuickTime also adds itself to the Notification Area but only
displays a config screen and not the actual application when double clicking
it. There is a lot of inconsistency and anything but a standard on the
behavior of Notification Area icons.
You can debate if the Outlook Notification Area icon is there for (end-user)
functional reasons or for informational reasons. The context menu doesn't
offer much everyday functionality but mainly connectivity settings and the
icon itself represents the connectivity state of Outlook. Most applications
that load a Notification Area icon for configuration purposes and status
indication, unload their icon when you close the main application. In that
sense; Outlook's behavior is according to that "standard." The "Hide when
minimized" feature should then of course be considered as an extra.
The analogy with Word, Excel and PowerPoint doesn't fly either; when you
close the last Word window, Word will close just as Outlook. When you have
multiple Word windows open and close 1, Word will remain running. Outlook
behaves the same when you have multiple main Outlook windows open.
Anyway, as there are no standards on the behavior of Notification Area
icons, the Product Managers are free to do whatever they want with it. No
need to get "infuriated" about it. If you think it should be standardized
you can pick it up with the Windows team that deals with guidelines,
standards and certifications. For requesting it as an Outlook feature you
can provide feedback to the Outlook team.
The current guideline for using Notification Area icons is;
Notification area. Use only for system and program features that have no
presence on the desktop, as well as a short-term source for notifications
and status. Any other usage should be optional, unselected by default.
source;
http://msdn2.microsoft.com/en-us/library/aa511448.aspx