Breaking down your post/questions regarding what DNN can and cannot do:

1. Auto publish and/or un-publish a page at a certain date/time.
    
   Yes.  This is already built into DNN.  Each page has a SETTINGS screen with options for "BEGIN DATE" and "END DATE".  Likewise, individual modules can have begin and end dates as well.  The limitation here is that only someone with page/module edit rights can access SETTINGS and set the values.
    
2. Subordinates can create pages.
    
   Yes.  You can assign roles to allow page creation.  The easiest thing is to assign the "ADMIN" role but this also gives access to user accounts, site settings, etc (more access than you want to grant).  In DNN 5.x you can grant access to the PAGES/TABS module without granting access to any other admin-level modules.  For DNN 4.x you have to fool DNN into thinking the PAGES/TABS module is a regular module as shown in the following post:  http://eguanasolutions.com/Blog/tabid/54/EntryID/16/default.aspx
    
3. Workflow (Managed Content Approval Process with Automated Email Notifications)
    
   No (and yes).  DNN by itself does not offer any type of workflow process.  Fotunately you can add (pay for) this feature through third-party modules.  One of the newer, better modules to offer this is Engage's Publish:  http://www.engagemodules.com/Modules/EngagePublish.aspx
    
   DNN is not a full-fledged CMS -- it has no support for content revisioning.  The Publish module provides this feature in addition to the content workflow/approval process.  There are more features/benefits as well, but workflow and revisioning are the two big ones IMO.  Also, Engage generally offers very good support for their products.  (In fact, if you need a crash-course in DNN administration and are willing to pay, Engage offers that service as well.)  At $300 Publish is not cheap by DNN standards but, by software development standards, $300 is not much at all considering developers typically charge between $50 to $130 an hour.  Considering that DNN itself is free, a total cost of $300 is a great deal for what you get.
    
   Note:  I am not affiliated with Engage -- I just like their products.  I will happily write a full review of Publish v5.3 if Engage sends over a free copy.  Anyone?....Anyone......?  :)

 
-mamlin