I kinda feel like I've derailed this thread with all this talk about the merits of Prequels so think I should direct everyone who wishes to continue the discussion over here:

http://originaltrilogy.com/forum/topic.cfm/Article-on-prequel-films-Note-Does-not-pertain-to-Godfather-II-which-isnt-a-prequel-its-a-sequel-with-extended-flashback-sequences-or-a-partial-prequel-to-some/post/451673/#TopicPost451673

As for Blade Runner, it's a film with a very specific style that I don't believe can be replicated by a modern day Sequel or Prequel. However, this move has very little to do with the artistic merit of extending the franchise and a lot to do with the business side of ensuring the rights to Blade Runner don't expire. This is why the news has been greeted negatively by the vast majority of fans.