First you should know that Outlook Express and Outlook are NOT the same product (although similar).
For example Outlook Express has a news reader (hence the question you got). A newsreader is used for looking at forums etc. If you DONT do this then no problem, but note that Outlook does NOT have a newsreader.
Also, it is VERY difficult (almost impossible) to set Outlook up so that it can look at two different people's e-mails, whereas you can easily do this with Outlook Express. If you only ever look at one persons e-mails with Outlook then again no problem.
Outlook DOES have a calendar, which Outlook Express does not, but apart from that I doubt you see much difference.