Hello Rguachey,
If you decide to go to install Windows 7, then Windows Mail or any email client is not currently included in Windows 7. Windows Live Mail will then be the email client that will be the most common one to install with Windows 7.
Windows Live Mail has a automatic new message notification as well with a tray icon.
Sure you could manually add Windows Mail to Windows 7, but Windows Mail is no longer being supported by Microsoft.
Hope this helps answer why.
Shawn