From what I can see Outlook defaults it's meeting length to the time period breakdown shown in the calendar. For example I use 15 minute increments so my default is 15 minutes. I really appreciate the message in the 45 minute meeting podcast but the discussion about defaults could be confusing to some people. It certainly took me 20 minutes to work out why I couldn't find a default setting.
To change the default calendar increment go via the view, current view and other settings in version 2003.
If a newer version has a default let me know