The Dedicated server is a stand-alone app, but it is only 49KB in size, so it requires the rest of the installation to work.
Foil: check your PMs.
The release date has changed, not because of any slip in the schedule, or any problems whatsoever. Cadenza's research has shown that indie-games released before Christmas get buried in the massive wave of big-name games which hit the shelves at that time. So the team will have the game ready ahead of Christmas, and take a well-deserved holiday, before the game officially ships - presumably mid-January.
A full Steam release while occur simultaneously.
If you are purchasing the game, please buy it directly from Cadenza, at
http://cadenzainteractive.com/buy-retrovirus/ as, obviously, they make more money if you do that. And I think we are all agreed we want Cadenza to do well out of Retrovirus.